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      3  1.1  christos <head>
      4  1.1  christos <title>Sources for time zone and daylight saving time data</title>
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     10  1.1  christos <body>
     11  1.1  christos <h1>Sources for time zone and daylight saving time data</h1>
     12  1.1  christos <p>
     13  1.1  christos <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
     14  1.1  christos <a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
     15  1.1  christos rules are controlled by individual
     16  1.1  christos governments. They are sometimes changed with little notice, and their
     17  1.1  christos histories and planned futures are often recorded only fitfully. Here
     18  1.1  christos is a summary of attempts to organize and record relevant data in this
     19  1.1  christos area.
     20  1.1  christos </p>
     21  1.6  christos   <h3>Outline</h3>
     22  1.6  christos   <nav>
     23  1.6  christos     <ul>
     24  1.6  christos       <li>The <code><abbr>tz</abbr></code> database product and process
     25  1.6  christos 	<ul>
     26  1.6  christos 	  <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li>
     27  1.6  christos 	  <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li>
     28  1.6  christos 	  <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li>
     29  1.6  christos 	  <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li>
     30  1.6  christos 	</ul>
     31  1.6  christos       </li>
     32  1.6  christos       <li>Uses of the <code><abbr>tz</abbr></code> database
     33  1.6  christos 	<ul>
     34  1.6  christos 	  <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li>
     35  1.6  christos 	  <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li>
     36  1.6  christos 	  <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li>
     37  1.6  christos 	  <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li>
     38  1.6  christos 	  <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li>
     39  1.6  christos 	</ul>
     40  1.6  christos       </li>
     41  1.6  christos       <li>Related data
     42  1.6  christos 	<ul>
     43  1.6  christos 	  <li><a href="#other-dbs">Other time zone databases</a></li>
     44  1.6  christos 	  <li><a href="#maps">Maps</a></li>
     45  1.6  christos 	  <li><a href="#boundaries">Time zone boundaries</a></li>
     46  1.6  christos 	</ul>
     47  1.6  christos       </li>
     48  1.6  christos       <li>Timekeeping concepts
     49  1.6  christos 	<ul>
     50  1.6  christos 	  <li><a href="#civil">Civil time concepts and history</a></li>
     51  1.6  christos 	  <li><a href="#national">National histories of legal time</a></li>
     52  1.6  christos 	  <li><a href="#precision">Precision timekeeping</a></li>
     53  1.6  christos 	  <li><a href="#notation">Time notation</a></li>
     54  1.6  christos 	  <li><a href="#see-also">See also</a></li>
     55  1.6  christos 	</ul>
     56  1.6  christos       </li>
     57  1.6  christos     </ul>
     58  1.6  christos   </nav>
     59  1.6  christos 
     60  1.6  christos <section>
     61  1.1  christos <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
     62  1.1  christos <p>
     63  1.1  christos The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
     64  1.1  christos time zone database contains code and data
     65  1.1  christos that represent the history of local time
     66  1.1  christos for many representative locations around the globe.
     67  1.1  christos It is updated periodically to reflect changes made by political bodies
     68  1.1  christos to time zone boundaries and daylight saving rules.
     69  1.1  christos This database (known as <code><abbr>tz</abbr></code>,
     70  1.1  christos <code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)
     71  1.1  christos is used by several implementations,
     72  1.1  christos including
     73  1.1  christos <a href="https://www.gnu.org/software/libc/">the
     74  1.1  christos <abbr title="GNU's Not Unix">GNU</abbr>
     75  1.1  christos C Library</a> (used in
     76  1.1  christos <a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),
     77  1.1  christos <a href="https://www.android.com">Android</a>,
     78  1.1  christos <a href="https://www.freebsd.org">Free<abbr
     79  1.1  christos title="Berkeley Software Distribution">BSD</abbr></a>,
     80  1.1  christos <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
     81  1.1  christos <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
     82  1.1  christos <a href="https://www.chromium.org/chromium-os">Chromium OS</a>,
     83  1.1  christos <a href="https://cygwin.com">Cygwin</a>,
     84  1.1  christos <a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
     85  1.1  christos <a href="https://www.mysql.com">MySQL</a>,
     86  1.1  christos <a href="https://en.wikipedia.org/wiki/WebOS"><abbr
     87  1.1  christos title="Web Operating System">webOS</abbr></a>,
     88  1.1  christos <a href="https://ibm.com/aix"><abbr
     89  1.1  christos title="Advanced Interactive eXecutive">AIX</abbr></a>,
     90  1.1  christos <a href="https://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>,
     91  1.6  christos <a href="https://www.apple.com/ios"><abbr
     92  1.1  christos title="iPhone OS">iOS</abbr></a>,
     93  1.6  christos <a href="https://www.apple.com/macos">macOS</a>,
     94  1.1  christos <a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,
     95  1.6  christos <a href="https://www.vmssoftware.com">Open<abbr
     96  1.1  christos title="Virtual Memory System">VMS</abbr></a>,
     97  1.6  christos <a href="https://www.oracle.com/database/">Oracle Database</a>, and
     98  1.1  christos <a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>
     99  1.1  christos <p>
    100  1.2  christos Each main entry in the database represents a <dfn>timezone</dfn>
    101  1.2  christos for a set of civil-time clocks that have all agreed since 1970.
    102  1.2  christos Timezones are typically identified by continent or ocean and then by the
    103  1.2  christos name of the largest city within the region containing the clocks.
    104  1.1  christos For example, <code>America/New_York</code>
    105  1.1  christos represents most of the <abbr title="United States">US</abbr> eastern time zone;
    106  1.1  christos <code>America/Phoenix</code> represents most of Arizona, which
    107  1.2  christos uses mountain time without daylight saving time (<abbr>DST</abbr>);
    108  1.1  christos <code>America/Detroit</code> represents most of Michigan, which uses
    109  1.1  christos eastern time but with different <abbr>DST</abbr> rules in 1975;
    110  1.1  christos and other entries represent smaller regions like Starke County,
    111  1.1  christos Indiana, which switched from central to eastern time in 1991
    112  1.1  christos and switched back in 2006.
    113  1.1  christos To use the database on an extended <a
    114  1.1  christos href="https://en.wikipedia.org/wiki/POSIX"><abbr
    115  1.1  christos title="Portable Operating System Interface">POSIX</abbr></a>
    116  1.1  christos implementation set the <code><abbr>TZ</abbr></code>
    117  1.1  christos environment variable to the location's full name,
    118  1.1  christos e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p>
    119  1.1  christos <p>
    120  1.2  christos Associated with each timezone is a history of offsets from
    121  1.1  christos <a href="https://en.wikipedia.org/wiki/Universal_Time">Universal
    122  1.1  christos Time</a> (<abbr>UT</abbr>), which is <a
    123  1.1  christos href="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean
    124  1.1  christos Time</a> (<abbr>GMT</abbr>) with days beginning at midnight;
    125  1.2  christos for timestamps after 1960 this is more precisely <a
    126  1.1  christos href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated
    127  1.1  christos Universal Time</a> (<abbr>UTC</abbr>).
    128  1.1  christos The database also records when daylight saving time was in use,
    129  1.1  christos along with some time zone abbreviations such as <abbr>EST</abbr>
    130  1.1  christos for Eastern Standard Time in the <abbr>US</abbr>.</p>
    131  1.6  christos </section>
    132  1.6  christos 
    133  1.6  christos <section>
    134  1.1  christos <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>
    135  1.1  christos <p>
    136  1.1  christos The following <a
    137  1.1  christos href="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download
    138  1.1  christos the latest release's two
    139  1.1  christos <a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a>
    140  1.1  christos to a <abbr>GNU</abbr>/Linux or similar host.</p>
    141  1.2  christos <pre><code>mkdir tzdb
    142  1.1  christos cd tzdb
    143  1.1  christos <a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
    144  1.1  christos wget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
    145  1.1  christos <a href="https://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="https://www.gnu.org/software/tar/">tar</a> -xf -
    146  1.1  christos gzip -dc tzdata-latest.tar.gz | tar -xf -
    147  1.1  christos </code></pre>
    148  1.1  christos <p>Alternatively, the following shell commands download the same
    149  1.1  christos release in a single-tarball format containing extra data
    150  1.1  christos useful for regression testing:</p>
    151  1.2  christos <pre><code>wget <a href="https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz">https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz</a>
    152  1.1  christos <a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -
    153  1.1  christos </code></pre>
    154  1.1  christos <p>These commands use convenience links to the latest release
    155  1.1  christos of the <code><abbr>tz</abbr></code> database hosted by the
    156  1.1  christos <a href="https://www.iana.org/time-zones">Time Zone Database website</a>
    157  1.1  christos of the <a href="https://www.iana.org">Internet Assigned Numbers
    158  1.1  christos Authority (IANA)</a>.
    159  1.1  christos Older releases are in files named
    160  1.1  christos <code>tzcode<var>V</var>.tar.gz</code>,
    161  1.1  christos <code>tzdata<var>V</var>.tar.gz</code>, and
    162  1.1  christos <code>tzdb-<var>V</var>.tar.lz</code>,
    163  1.1  christos where <code><var>V</var></code> is the version.
    164  1.1  christos Since 1996, each version has been a four-digit year followed by
    165  1.1  christos lower-case letter (<samp>a</samp> through <samp>z</samp>,
    166  1.1  christos then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>
    167  1.1  christos through <samp>zzz</samp>, and so on).
    168  1.1  christos Since version 2016h, each release has contained a text file named
    169  1.1  christos "<samp>version</samp>" whose first (and currently only) line is the version.
    170  1.1  christos The releases are also available in an
    171  1.1  christos <a href="ftp://ftp.iana.org/tz/releases/"><abbr
    172  1.1  christos title="File Transfer Protocol">FTP</abbr> directory</a> via a
    173  1.1  christos less-secure protocol.</p>
    174  1.1  christos <p>Alternatively, a development repository of code and data can be
    175  1.1  christos retrieved from <a href="https://github.com">GitHub</a> via the shell
    176  1.1  christos command:</p>
    177  1.2  christos <pre><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a>
    178  1.1  christos </code></pre>
    179  1.1  christos <p>
    180  1.1  christos Since version 2012e, each release has been tagged in development repositories.
    181  1.1  christos Untagged commits are less well tested and probably contain
    182  1.1  christos more errors.</p>
    183  1.1  christos <p>
    184  1.1  christos After obtaining the code and data files, see the
    185  1.1  christos <code>README</code> file for what to do next.
    186  1.1  christos The code lets you compile the <code><abbr>tz</abbr></code> source files into
    187  1.2  christos machine-readable binary files, one for each location. The binary files
    188  1.5  christos are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>)
    189  1.5  christos specified by <a href="https://tools.ietf.org/html/8536">Internet
    190  1.5  christos <abbr>RFC</abbr> 8536</a>.
    191  1.2  christos The code also lets
    192  1.2  christos you read a <abbr>TZif</abbr> file and interpret timestamps for that
    193  1.1  christos location.</p>
    194  1.6  christos </section>
    195  1.6  christos 
    196  1.6  christos <section>
    197  1.1  christos <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
    198  1.1  christos <p>
    199  1.1  christos The <code><abbr>tz</abbr></code> code and data
    200  1.1  christos are by no means authoritative. If you find errors, please
    201  1.1  christos send changes to <a href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a>,
    202  1.1  christos the time zone mailing list. You can also <a
    203  1.1  christos href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
    204  1.1  christos and browse the <a
    205  1.1  christos href="https://mm.icann.org/pipermail/tz/">archive of old
    206  1.5  christos messages</a>.
    207  1.5  christos <a href="https://tzdata-meta.timtimeonline.com/">Metadata for mailing list
    208  1.5  christos discussions</a> and corresponding data changes can be
    209  1.5  christos generated <a href="https://github.com/timparenti/tzdata-meta">automatically</a>.
    210  1.5  christos </p>
    211  1.1  christos <p>
    212  1.1  christos If your government plans to change its time zone boundaries or
    213  1.1  christos daylight saving rules, inform <code>tz (a] iana.org</code> well in
    214  1.1  christos advance, as this will coordinate updates to many cell phones,
    215  1.1  christos computers, and other devices around the world. With
    216  1.1  christos less than a year's notice there is a good chance that some
    217  1.1  christos computer-based clocks will operate incorrectly after the change, due
    218  1.1  christos to delays in propagating updates to software and data. The shorter
    219  1.1  christos the notice, the more likely clock problems will arise; see "<a
    220  1.1  christos href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
    221  1.1  christos the Timing of Time Zone Changes</a>" for examples.
    222  1.1  christos </p>
    223  1.1  christos <p>
    224  1.1  christos Changes to the <code><abbr>tz</abbr></code> code and data are often
    225  1.1  christos propagated to clients via operating system updates, so
    226  1.1  christos client <code><abbr>tz</abbr></code> data can often be corrected by
    227  1.1  christos applying these updates. With GNU/Linux and similar systems, if your
    228  1.1  christos maintenance provider has not yet adopted the
    229  1.1  christos latest <code><abbr>tz</abbr></code> data, you can often short-circuit
    230  1.1  christos the process by tailoring the generic instructions in
    231  1.1  christos the <code><abbr>tz</abbr> README</code> file and installing the latest
    232  1.1  christos data yourself. System-specific instructions for installing the
    233  1.1  christos latest <code><abbr>tz</abbr></code> data have also been published
    234  1.1  christos for <a href="https://www.ibm.com/developerworks/aix/library/au-aix-olson-time-zone/index.html"><abbr>AIX</abbr></a>,
    235  1.1  christos <a
    236  1.1  christos href="https://play.google.com/store/apps/details?id=com.google.android.timezone.data">Android</a>,
    237  1.1  christos <a
    238  1.1  christos href="http://userguide.icu-project.org/datetime/timezone"><abbr
    239  1.1  christos title="International Components for Unicode">ICU</abbr></a>,
    240  1.1  christos <a href="https://developer.ibm.com/javasdk/support/dst/jtzu/"><abbr>IBM</abbr></a>
    241  1.1  christos and <a
    242  1.4  christos href="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">Oracle</a>
    243  1.4  christos Java, <a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
    244  1.1  christos href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
    245  1.1  christos and <a
    246  1.1  christos href="https://nodatime.org/userguide/tzdb">Noda Time</a> (see below).
    247  1.1  christos </p>
    248  1.1  christos <p>Sources for the <code><abbr>tz</abbr></code> database are
    249  1.1  christos <a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
    250  1.1  christos title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
    251  1.1  christos <a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
    252  1.1  christos with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
    253  1.1  christos title="linefeed">LF</abbr></a>,
    254  1.1  christos which can be modified by common text editors such
    255  1.1  christos as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
    256  1.1  christos <a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
    257  1.1  christos <a href="https://www.vim.org">vim</a>.
    258  1.1  christos Specialized source-file editing can be done via the
    259  1.1  christos <a href="https://packagecontrol.io/packages/zoneinfo">Sublime
    260  1.1  christos zoneinfo</a> package for <a
    261  1.1  christos href="https://www.sublimetext.com">Sublime Text</a> and the <a
    262  1.1  christos href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
    263  1.1  christos zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
    264  1.1  christos Studio Code</a>.
    265  1.1  christos </p>
    266  1.1  christos <p>
    267  1.1  christos For further information about updates, please see
    268  1.1  christos <a href="https://tools.ietf.org/html/rfc6557">Procedures for
    269  1.1  christos Maintaining the Time Zone Database</a> (Internet <abbr
    270  1.1  christos title="Request For Comments">RFC</abbr> 6557). More detail can be
    271  1.1  christos found in <a href="theory.html">Theory and pragmatics of the tz code and data</a>.
    272  1.2  christos <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
    273  1.2  christos displays changes between recent <code><abbr>tzdb</abbr></code> versions.
    274  1.1  christos </p>
    275  1.6  christos </section>
    276  1.6  christos 
    277  1.6  christos <section>
    278  1.1  christos <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
    279  1.1  christos <ul>
    280  1.1  christos <li>The article
    281  1.1  christos <a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
    282  1.1  christos an encyclopedic summary.</li>
    283  1.1  christos <li><a href="tz-how-to.html">How to Read the
    284  1.1  christos tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
    285  1.1  christos database format.</li>
    286  1.1  christos <li><a
    287  1.1  christos href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
    288  1.1  christos literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
    289  1.1  christos database's style.</li>
    290  1.1  christos </ul>
    291  1.6  christos </section>
    292  1.6  christos 
    293  1.6  christos <section>
    294  1.1  christos <h2 id="web">Web sites using recent versions of the
    295  1.1  christos <code><abbr>tz</abbr></code> database</h2>
    296  1.1  christos <p>
    297  1.1  christos These are listed roughly in ascending order of complexity and fanciness.
    298  1.1  christos </p>
    299  1.1  christos <ul>
    300  1.1  christos <li><a href="https://time.is">Time.is</a> shows locations'
    301  1.1  christos time and zones.</li>
    302  1.1  christos <li><a href="https://www.timejones.com">TimeJones.com</a>,
    303  1.1  christos <a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
    304  1.6  christos <a href="https://worldclock.com">The World Clock</a>
    305  1.1  christos are time zone converters.</li>
    306  1.1  christos <li><a
    307  1.6  christos href="https://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
    308  1.1  christos lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
    309  1.1  christos <li><a
    310  1.1  christos href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
    311  1.1  christos Time in 1000 Places</a> uses descriptions of the values.</li>
    312  1.6  christos <li><a href="https://timezoneconverterapp.com/">Time Zone Converter</a>
    313  1.1  christos uses a pulldown menu.</li>
    314  1.1  christos <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete
    315  1.1  christos timezone information for all countries</a> displays tables of DST rules.
    316  1.1  christos <li><a href="https://www.timeanddate.com/worldclock/">The World Clock &ndash;
    317  1.1  christos Worldwide</a> lets you sort zone names and convert times.</li>
    318  1.1  christos <li><a href="https://24timezones.com">24TimeZones</a> has a world
    319  1.1  christos time map and a time converter.</li>
    320  1.1  christos <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
    321  1.1  christos calculates the current time difference between locations.</li>
    322  1.1  christos <li><a href="http://www.wx-now.com">Weather Now</a> and
    323  1.1  christos <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
    324  1.1  christos </ul>
    325  1.6  christos </section>
    326  1.6  christos 
    327  1.6  christos <section>
    328  1.1  christos <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
    329  1.1  christos <ul>
    330  1.1  christos <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
    331  1.1  christos <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
    332  1.1  christos Distribution Service (tzdist) working group</a> defined <a
    333  1.1  christos href="https://tools.ietf.org/html/rfc7808">TZDIST</a>
    334  1.1  christos (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
    335  1.1  christos along with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
    336  1.1  christos (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
    337  1.2  christos transferring time zone data by reference.
    338  1.2  christos The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
    339  1.6  christos mailing list</a> discussed the Internet draft <a
    340  1.1  christos id="TZDIST-Geolocate"
    341  1.2  christos href="https://tools.ietf.org/html/draft-murchison-tzdist-geolocate">TZDIST
    342  1.6  christos Geolocate Extension</a> (now expired), which let a client determine its timezone
    343  1.1  christos from its geographic location using a <a
    344  1.5  christos href="https://tools.ietf.org/html/rfc5870">'geo' URI</a>.</li>
    345  1.1  christos <li>The <a href="https://tools.ietf.org/html/rfc5545">
    346  1.1  christos Internet Calendaring and Scheduling Core Object Specification
    347  1.1  christos (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
    348  1.1  christos covers time zone
    349  1.1  christos data; see its VTIMEZONE calendar component.
    350  1.1  christos The iCalendar format requires specialized parsers and generators; a
    351  1.1  christos variant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
    352  1.1  christos (Internet <abbr>RFC</abbr> 6321) uses
    353  1.1  christos <a href="https://www.w3.org/XML/"><abbr
    354  1.1  christos title="Extensible Markup Language">XML</abbr></a> format, and a variant
    355  1.1  christos <a href="https://tools.ietf.org/html/rfc7265">jCal</a>
    356  1.1  christos (Internet <abbr>RFC</abbr> 7265)
    357  1.1  christos uses <a href="https://www.json.org"><abbr
    358  1.1  christos title="JavaScript Object Notation">JSON</abbr></a> format.</li>
    359  1.1  christos </ul>
    360  1.6  christos </section>
    361  1.6  christos 
    362  1.6  christos <section>
    363  1.1  christos <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
    364  1.1  christos <ul>
    365  1.1  christos <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
    366  1.1  christos href="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>
    367  1.1  christos program that compiles
    368  1.1  christos <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
    369  1.1  christos Vzic is freely
    370  1.1  christos available under the <a
    371  1.1  christos href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
    372  1.1  christos General Public License (<abbr
    373  1.1  christos title="General Public License">GPL</abbr>)</a>.</li>
    374  1.1  christos <li><a href="https://sourceforge.net/projects/tzical/">tziCal &ndash; tz
    375  1.1  christos database conversion utility</a> is like Vzic, except for the <a
    376  1.6  christos href="https://dotnet.microsoft.com">.NET framework</a>
    377  1.1  christos and with a <abbr>BSD</abbr>-style license.</li>
    378  1.1  christos <li><a
    379  1.4  christos href="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>
    380  1.1  christos contains a script <code>parse_olson</code> that compiles
    381  1.1  christos <code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
    382  1.1  christos modules. It is part of the Perl <a
    383  1.4  christos href="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>,
    384  1.4  christos which is freely
    385  1.1  christos available under both the <abbr>GPL</abbr> and the Perl Artistic
    386  1.1  christos License. DateTime::TimeZone also contains a script
    387  1.1  christos <code>tests_from_zdump</code> that generates test cases for each clock
    388  1.1  christos transition in the <code><abbr>tz</abbr></code> database.</li>
    389  1.1  christos <li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
    390  1.1  christos Database Parser</a> is a
    391  1.1  christos <a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
    392  1.1  christos runtime library that is <a
    393  1.1  christos href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0355r4.html">moving
    394  1.6  christos forward</a> for inclusion in
    395  1.6  christos <a href="https://en.wikipedia.org/wiki/C++20">C++20</a>,
    396  1.6  christos the next iteration of the C++ standard.
    397  1.1  christos It is freely available under the
    398  1.1  christos <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
    399  1.1  christos <li><a id="ICU" href="http://site.icu-project.org">International Components for
    400  1.1  christos Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
    401  1.1  christos href="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>
    402  1.1  christos libraries for internationalization that
    403  1.1  christos has a compiler from <code><abbr>tz</abbr></code> source
    404  1.1  christos and from <abbr title="Common Locale Data Repository">CLDR</abbr> data
    405  1.1  christos (mentioned <a href="#CLDR">below</a>)
    406  1.1  christos into an <abbr>ICU</abbr>-specific format.
    407  1.1  christos <abbr>ICU</abbr> is freely available under a
    408  1.1  christos <abbr>BSD</abbr>-style license.</li>
    409  1.1  christos <li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
    410  1.1  christos the <a href="https://elixir-lang.org">Elixir</a> language downloads
    411  1.1  christos and compiles tz source and exposes <abbr
    412  1.1  christos title="Application Program Interface">API</abbr>s for use. It is
    413  1.1  christos freely available under the <abbr>MIT</abbr> license.</li>
    414  1.1  christos <li>Java-based compilers and libraries include:
    415  1.1  christos <ul>
    416  1.1  christos <li>The <a
    417  1.4  christos href="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater
    418  1.1  christos tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
    419  1.1  christos Oracle Java.</li>
    420  1.1  christos <li>The <a
    421  1.4  christos href="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
    422  1.6  christos SE 8 Date and Time</a> <abbr>API</abbr> can be supplemented by <a
    423  1.4  christos href="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
    424  1.1  christos which is freely available under a <abbr>BSD</abbr>-style license.</li>
    425  1.4  christos <li><a href="https://www.joda.org/joda-time/">Joda-Time &ndash; Java date
    426  1.1  christos and time <abbr>API</abbr></a> contains a class
    427  1.1  christos <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
    428  1.1  christos <code><abbr>tz</abbr></code> source into a binary format. It inspired
    429  1.1  christos Java 8 <code>java.time</code>, which its users should migrate to once
    430  1.1  christos they can assume Java 8 or later. It is available under the <a
    431  1.1  christos href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
    432  1.4  christos <li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and
    433  1.4  christos time library for Android</a> and
    434  1.4  christos <a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date,
    435  1.4  christos time and interval library for Java</a> compile
    436  1.4  christos <code><abbr>tz</abbr></code> source into a binary format.
    437  1.4  christos Time4A is available under the Apache License and Time4J is
    438  1.1  christos available under the <a
    439  1.1  christos href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
    440  1.1  christos General Public License (<abbr title="Lesser General Public
    441  1.1  christos License">LGPL</abbr>)</a>.</li>
    442  1.1  christos <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
    443  1.1  christos Java-based libraries.</li>
    444  1.1  christos </ul>
    445  1.1  christos <li><a href="https://nodatime.org">Noda Time &ndash; Date and
    446  1.1  christos time <abbr>API</abbr> for .NET</a>
    447  1.4  christos is like Joda-Time and Time4J, but for the .NET framework instead of Java.
    448  1.4  christos It is freely available under the Apache License.</li>
    449  1.1  christos <li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based
    450  1.1  christos compilers and libraries include:
    451  1.1  christos <ul>
    452  1.1  christos <li><a
    453  1.1  christos href="https://github.com/kshetline/compact-time-zone-generator">CompactTimeZoneGenerator</a>
    454  1.1  christos compiles time zone data into a compact form designed for
    455  1.1  christos JavaScript. It is freely available under a combination of
    456  1.1  christos the <abbr>MIT</abbr> license and the Apache License.</li>
    457  1.1  christos <li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
    458  1.1  christos plugin for the <a href="https://momentjs.com">Moment.js</a> date
    459  1.1  christos manipulation library. It is freely available under the <abbr>MIT</abbr>
    460  1.1  christos license.</li>
    461  1.1  christos <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s
    462  1.1  christos <abbr>API</abbr> is upward compatible with standard JavaScript
    463  1.1  christos Dates. It is freely available under the Apache License.</li>
    464  1.1  christos </ul>
    465  1.1  christos <li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
    466  1.1  christos compiler from <code><abbr>tz</abbr></code> source into
    467  1.1  christos <a href="https://julialang.org/">Julia</a>. It is freely available
    468  1.1  christos under the <abbr>MIT</abbr> license.</li>
    469  1.6  christos <li><a href="https://github.com/pavkam/tzdb"><abbr>TZDB</abbr> &ndash;
    470  1.6  christos <abbr>IANA</abbr> Time Zone Database for Delphi/<abbr
    471  1.6  christos title="Free Pascal Compiler">FPC</abbr></a>
    472  1.2  christos compiles from <code><abbr>tz</abbr></code> source into
    473  1.2  christos <a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>
    474  1.2  christos as compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>
    475  1.2  christos and <a
    476  1.2  christos href="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.
    477  1.2  christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
    478  1.1  christos <li><a href="http://pytz.sourceforge.net">pytz &ndash; World Timezone
    479  1.1  christos Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
    480  1.1  christos <a href="https://www.python.org">Python</a>.
    481  1.1  christos It is freely available under a <abbr>BSD</abbr>-style license.</li>
    482  1.1  christos <li><a href="https://tzinfo.github.io">TZInfo &ndash;
    483  1.1  christos Ruby Timezone Library</a>
    484  1.1  christos compiles <code><abbr>tz</abbr></code> source into
    485  1.1  christos <a href="https://www.ruby-lang.org/en/">Ruby</a>.
    486  1.1  christos It is freely available under the <abbr>MIT</abbr> license.</li>
    487  1.1  christos <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
    488  1.1  christos Library</a> is
    489  1.1  christos a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
    490  1.1  christos library that compiles <code><abbr>tz</abbr></code> source into a time
    491  1.1  christos zone repository whose format
    492  1.1  christos is either proprietary or an <abbr>XML</abbr>-encoded
    493  1.1  christos representation.</li>
    494  1.1  christos <li><a id="Tcl" href="https://tcl.tk">Tcl</a>
    495  1.1  christos contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
    496  1.1  christos source into text files, along with a runtime that can read those
    497  1.1  christos files. Tcl is freely available under a <abbr>BSD</abbr>-style
    498  1.1  christos license.</li>
    499  1.1  christos </ul>
    500  1.6  christos </section>
    501  1.6  christos 
    502  1.6  christos <section>
    503  1.2  christos <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
    504  1.1  christos <ul>
    505  1.1  christos <li>The <a
    506  1.1  christos href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
    507  1.1  christos Library</a>
    508  1.1  christos has an independent, thread-safe implementation of
    509  1.2  christos a <abbr>TZif</abbr> file reader.
    510  1.1  christos This library is freely available under the LGPL
    511  1.1  christos and is widely used in <abbr>GNU</abbr>/Linux systems.</li>
    512  1.1  christos <li><a href="https://www.gnome.org">GNOME</a>'s
    513  1.1  christos <a href="https://developer.gnome.org/glib/">GLib</a> has
    514  1.2  christos a <abbr>TZif</abbr> file reader written in C that
    515  1.1  christos creates a <code>GTimeZone</code> object representing sets
    516  1.1  christos of <abbr>UT</abbr> offsets.
    517  1.1  christos It is freely available under the <abbr>LGPL</abbr>.</li>
    518  1.1  christos <li>The
    519  1.1  christos <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
    520  1.1  christos <code>baltzo::TimeZoneUtil</code> component contains a C++
    521  1.2  christos implementation of a <abbr>TZif</abbr> file reader. It is freely available under
    522  1.1  christos the Apache License.</li>
    523  1.1  christos <li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
    524  1.1  christos library that translates between <abbr>UT</abbr> and civil time and
    525  1.2  christos can read <abbr>TZif</abbr> files. It is freely available under the Apache
    526  1.1  christos License.</li>
    527  1.1  christos <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a>
    528  1.2  christos is a <abbr>TZif</abbr> file reader written in Java.
    529  1.1  christos It is freely available under the <abbr>LGPL</abbr>.</li>
    530  1.1  christos <li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
    531  1.2  christos library that reads <abbr>TZif</abbr> files and converts
    532  1.2  christos timestamps from one time zone or format to another.
    533  1.1  christos It is used by <a href="https://secure.php.net"><abbr
    534  1.1  christos title="PHP: Hypertext Preprocessor">PHP</abbr></a>,
    535  1.1  christos <a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
    536  1.1  christos and <a href="https://www.mongodb.com">MongoDB</a>.
    537  1.1  christos It is freely available under the <abbr>MIT</abbr> license.</li>
    538  1.1  christos <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
    539  1.1  christos JavaScript library that supports date arithmetic that is time zone
    540  1.1  christos aware. It is freely available under the <abbr>MIT</abbr> license.</li>
    541  1.1  christos <li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
    542  1.2  christos <abbr>TZif</abbr> file reader.</li>
    543  1.4  christos <li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile">
    544  1.1  christos DateTime::TimeZone::Tzfile</a>
    545  1.2  christos is a <abbr>TZif</abbr> file reader written in Perl.
    546  1.1  christos It is freely available under the same terms as Perl
    547  1.1  christos (dual <abbr>GPL</abbr> and Artistic license).</li>
    548  1.1  christos <li>The
    549  1.1  christos public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
    550  1.1  christos library contains a Python tool that
    551  1.2  christos converts <abbr>TZif</abbr> data into
    552  1.1  christos <abbr>JSON</abbr>-format data suitable for use
    553  1.1  christos in its JavaScript library for time zone conversion. Dates before 1970
    554  1.1  christos are not supported.</li>
    555  1.1  christos <li>The <a
    556  1.1  christos href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
    557  1.1  christos package contains <a href="https://www.haskell.org">Haskell</a> code that
    558  1.2  christos parses and uses <abbr>TZif</abbr> data. It is freely
    559  1.1  christos available under a <abbr>BSD</abbr>-style license.</li>
    560  1.1  christos </ul>
    561  1.6  christos </section>
    562  1.6  christos 
    563  1.6  christos <section>
    564  1.1  christos <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
    565  1.1  christos <ul>
    566  1.1  christos <li><a href="https://foxclocks.org">FoxClocks</a>
    567  1.1  christos is an extension for <a href="https://www.google.com/chrome/">Google
    568  1.1  christos Chrome</a> and for <a
    569  1.1  christos href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla
    570  1.1  christos Toolkit</a> applications like <a
    571  1.1  christos href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
    572  1.1  christos href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
    573  1.1  christos It displays multiple clocks in the application window, and has a mapping
    574  1.1  christos interface to <a href="https://www.google.com/earth/">Google Earth</a>.
    575  1.1  christos It is freely available under the <abbr>GPL</abbr>.</li>
    576  1.1  christos <li><a href="https://golang.org">Go programming language</a>
    577  1.1  christos implementations contain a copy of a 32-bit subset of a recent
    578  1.1  christos <code><abbr>tz</abbr></code> database in a
    579  1.1  christos Go-specific format.</li>
    580  1.1  christos <li><a
    581  1.1  christos href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International
    582  1.1  christos clock (intclock)</a> is a clock that displays multiple time zones on
    583  1.1  christos <abbr>GNU</abbr>/Linux and similar systems. It is freely available
    584  1.1  christos under the <abbr>GPL</abbr>.</li>
    585  1.1  christos <li>Microsoft Windows 8.1
    586  1.1  christos and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
    587  1.3  christos data (mentioned <a href="#CLDR">below</a>) used by the
    588  1.3  christos <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /
    589  1.3  christos <a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes
    590  1.3  christos <a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and
    591  1.3  christos <a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.
    592  1.1  christos <a id="System.TimeZoneInfo"
    593  1.1  christos href="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
    594  1.1  christos Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
    595  1.1  christos the older, proprietary method of Microsoft Windows 2000 and later,
    596  1.1  christos which stores time zone data in the
    597  1.1  christos <a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
    598  1.1  christos <a
    599  1.1  christos href="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone &rarr;
    600  1.1  christos Tzid table</a> or <a
    601  1.6  christos href="https://github.com/unicode-org/cldr/blob/master/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
    602  1.1  christos file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
    603  1.1  christos to <code><abbr>tz</abbr></code> names.
    604  1.3  christos These mappings can be performed programmatically via the <a href="https://github.com/mj1856/TimeZoneConverter">TimeZoneConverter</a> .NET library,
    605  1.3  christos or the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.
    606  1.1  christos <li><a
    607  1.1  christos href="https://www.oracle.com/java/index.html">Oracle
    608  1.1  christos Java</a> contains a copy of a subset of a recent
    609  1.1  christos <code><abbr>tz</abbr></code> database in a
    610  1.1  christos Java-specific format.</li>
    611  1.2  christos <li><a href="https://relativedata.com/page/Time-Zone-Master">Time Zone
    612  1.1  christos Master</a> is a Microsoft Windows clock program that can automatically
    613  1.4  christos download, compile and use <code><abbr>tz</abbr></code> releases.
    614  1.4  christos The Basic version is free.</li>
    615  1.1  christos <li><a
    616  1.1  christos href="http://veladg.com/velaterra.html">VelaTerra</a> is
    617  1.1  christos a macOS program. Its developers
    618  1.1  christos <a href="http://veladg.com/tzoffer.html">offer free
    619  1.1  christos licenses</a> to <code><abbr>tz</abbr></code> contributors.</li>
    620  1.1  christos </ul>
    621  1.6  christos </section>
    622  1.6  christos 
    623  1.6  christos <section>
    624  1.1  christos <h2 id="other-dbs">Other time zone databases</h2>
    625  1.1  christos <ul>
    626  1.1  christos <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
    627  1.4  christos is Astrodienst's Web version of Shanks and Pottenger's out-of-print
    628  1.4  christos time zone history atlases
    629  1.4  christos <a href="https://www.worldcat.org/oclc/468828649">for the US</a> and
    630  1.4  christos <a href="https://www.worldcat.org/oclc/76950459">for the world</a>,
    631  1.4  christos now published in <a
    632  1.1  christos href="https://astrocom.com/astrology-products/software/acs-atlas-software">software</a>
    633  1.1  christos form by <a href="https://astrocom.com">ACS-Starcrafts</a>.
    634  1.4  christos Although these extensive atlases
    635  1.4  christos <a href="https://astrologynewsservice.com/opinion/how-astrologers-contributed-to-the-information-age-a-brief-history-of-time/">were
    636  1.4  christos sources for much of the older <code><abbr>tz</abbr></code> data</a>,
    637  1.4  christos they are unreliable as Shanks appears to have
    638  1.1  christos guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
    639  1.1  christos sources and do not indicate which entries are guesswork.</li>
    640  1.1  christos <li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
    641  1.1  christos its own <code>tztab</code>(4) format.</li>
    642  1.1  christos <li>Microsoft Windows has proprietary data mentioned
    643  1.1  christos <a href="#System.TimeZoneInfo">above</a>.</li>
    644  1.1  christos <li><a href="https://www.worldtimeserver.com">World Time Server</a>
    645  1.1  christos is another time zone database.</li>
    646  1.1  christos <li>The <a
    647  1.1  christos href="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
    648  1.1  christos Schedules Information Manual</a> of the
    649  1.1  christos International Air Transport Association
    650  1.1  christos gives current time zone rules for airports served by commercial aviation.</li>
    651  1.1  christos </ul>
    652  1.6  christos </section>
    653  1.6  christos 
    654  1.6  christos <section>
    655  1.1  christos <h2 id="maps">Maps</h2>
    656  1.1  christos <ul>
    657  1.1  christos <li>The <a href="https://www.cia.gov/index.html">United States Central
    658  1.1  christos Intelligence Agency (<abbr
    659  1.1  christos title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a
    660  1.1  christos href="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time
    661  1.1  christos zone map</a>; the
    662  1.1  christos <a
    663  1.6  christos href="https://legacy.lib.utexas.edu/maps/world.html">Perry&ndash;Casta&ntilde;eda
    664  1.1  christos Library Map Collection</a>
    665  1.1  christos of the University of Texas at Austin has copies of
    666  1.1  christos recent editions.
    667  1.1  christos The pictorial quality is good,
    668  1.1  christos but the maps do not indicate daylight saving time,
    669  1.1  christos and parts of the data are a few years out of date.</li>
    670  1.6  christos <li><a href="https://www.worldtimezone.com">World Time Zone Map
    671  1.6  christos with current time</a>
    672  1.1  christos has several fancy time zone maps; it covers Russia particularly well.
    673  1.1  christos The maps' pictorial quality is not quite as good as the
    674  1.1  christos <abbr>CIA</abbr>'s
    675  1.1  christos but the maps are more up to date.</li>
    676  1.1  christos <li><a
    677  1.1  christos href="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
    678  1.1  christos much is time wrong around the world?</a> maps the difference between
    679  1.1  christos mean solar and standard time, highlighting areas such as western China
    680  1.1  christos where the two differ greatly. It's a bit out of date, unfortunately.</li>
    681  1.1  christos </ul>
    682  1.6  christos </section>
    683  1.6  christos 
    684  1.6  christos <section>
    685  1.1  christos <h2 id="boundaries">Time zone boundaries</h2>
    686  1.2  christos <p>Geographical boundaries between timezones are available
    687  1.1  christos from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a>
    688  1.1  christos services and other sources.</p>
    689  1.1  christos <ul>
    690  1.1  christos <li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
    691  1.1  christos Boundary Builder</a> extracts
    692  1.1  christos <a href="https://www.openstreetmap.org">Open Street Map</a> data to build
    693  1.2  christos boundaries of <code><abbr>tzdb</abbr></code> timezones.
    694  1.1  christos Its code is freely available under the <abbr>MIT</abbr> license, and
    695  1.1  christos its data entries are freely available under the
    696  1.1  christos <a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
    697  1.1  christos Open Database License</a>. The maps' borders appear to be quite accurate.</li>
    698  1.1  christos <li>Programmatic interfaces that map geographical coordinates via tz_world to
    699  1.2  christos <code><abbr>tzdb</abbr></code> timezones include:
    700  1.1  christos <ul>
    701  1.1  christos <li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
    702  1.1  christos written in <a
    703  1.1  christos href="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
    704  1.1  christos and is freely available under the <abbr>MIT</abbr> license.</li>
    705  1.1  christos <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
    706  1.1  christos is written in Go and is freely available under the Apache License.</li>
    707  1.1  christos <li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
    708  1.1  christos in both Java and
    709  1.1  christos <a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
    710  1.1  christos form, is freely available under the MIT license.</li>
    711  1.1  christos <li>For <a href="https://nodejs.org/en/">Node.js</a>,
    712  1.1  christos the <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
    713  1.1  christos is freely available under the MIT license, and
    714  1.1  christos the <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
    715  1.1  christos is in the public domain.</li>
    716  1.1  christos <li>The <a
    717  1.1  christos href="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
    718  1.1  christos library for Python is freely available under the MIT license.
    719  1.1  christos <li>The <a
    720  1.1  christos href="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
    721  1.1  christos library for Ruby is freely available under the MIT license.</li>
    722  1.1  christos </ul></li>
    723  1.1  christos <li>Free access via a network API, if you register a key, is provided by
    724  1.4  christos the <a
    725  1.4  christos href="https://www.geonames.org/export/web-services.html#timezone">GeoNames
    726  1.4  christos Timezone web service</a>, the <a
    727  1.4  christos href="https://developers.google.com/maps/documentation/timezone/intro">Google
    728  1.4  christos Maps Time Zone API</a>, and
    729  1.1  christos the <a href="https://timezonedb.com">Time Zone Database &amp; API</a>.
    730  1.1  christos Commercial network API access is provided
    731  1.1  christos by <a href="https://askgeo.com">AskGeo</a>
    732  1.1  christos and <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
    733  1.1  christos </li>
    734  1.1  christos <li>"<a
    735  1.1  christos href="https://stackoverflow.com/questions/16086962/how-to-get-a-time-zone-from-a-location-using-latitude-and-longitude-coordinates/16086964">How
    736  1.1  christos to get a time zone from a location using latitude and longitude
    737  1.1  christos coordinates?</a>" discusses other geolocation possibilities.</li>
    738  1.1  christos <li><a href="http://statoids.com/statoids.html">Administrative
    739  1.1  christos Divisions of Countries ("Statoids")</a> lists
    740  1.1  christos political subdivision data related to time zones.</li>
    741  1.1  christos <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time
    742  1.1  christos zone boundaries for multizone countries</a> summarizes legal
    743  1.1  christos boundaries between time zones within countries.</li>
    744  1.1  christos <li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
    745  1.1  christos &ndash; GIS and Database Tools</a> includes a Manifold-format map of
    746  1.1  christos world time zone boundaries distributed under the
    747  1.1  christos <abbr>GPL</abbr>.</li>
    748  1.1  christos <li>A ship within the <a
    749  1.1  christos href="https://en.wikipedia.org/wiki/Territorial_waters">territorial
    750  1.1  christos waters</a> of any nation uses that nation's time. In international
    751  1.1  christos waters, time zone boundaries are meridians 15&deg; apart, except that
    752  1.1  christos <abbr>UT</abbr>&minus;12 and <abbr>UT</abbr>+12 are each 7.5&deg;
    753  1.1  christos wide and are separated by
    754  1.1  christos the 180&deg; meridian (not by the International Date Line, which is
    755  1.1  christos for land and territorial waters only). A captain can change ship's
    756  1.1  christos clocks any time after entering a new time zone; midnight changes are
    757  1.1  christos common.</li>
    758  1.1  christos </ul>
    759  1.6  christos </section>
    760  1.6  christos 
    761  1.6  christos <section>
    762  1.1  christos <h2 id="civil">Civil time concepts and history</h2>
    763  1.1  christos <ul>
    764  1.1  christos <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
    765  1.1  christos Walk through Time</a>
    766  1.1  christos surveys the evolution of timekeeping.</li>
    767  1.4  christos <li>The history of daylight saving time is surveyed in <a
    768  1.4  christos href="http://www.webexhibits.org/daylightsaving/">About Daylight
    769  1.4  christos Saving Time &ndash; History, rationale, laws &amp; dates</a> and summarized in
    770  1.4  christos <a href="http://seizethedaylight.com/dst/">A Brief
    771  1.4  christos History of Daylight Saving Time</a>.</li>
    772  1.4  christos <li><a href="https://www.laphamsquarterly.org/roundtable/time-lords">Time
    773  1.4  christos Lords</a> discusses how authoritarians manipulate civil time.</li>
    774  1.1  christos <li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a>
    775  1.1  christos contains guidelines and best practices for software applications that
    776  1.1  christos deal with civil time.</li>
    777  1.1  christos <li><a href="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
    778  1.1  christos the International Date Line</a> tells the story of the most important
    779  1.1  christos time zone boundary.</li>
    780  1.1  christos <li><a href="http://statoids.com/tconcept.html">Basic Time
    781  1.1  christos Zone Concepts</a> discusses terminological issues behind time zones.</li>
    782  1.1  christos </ul>
    783  1.6  christos </section>
    784  1.6  christos 
    785  1.6  christos <section>
    786  1.1  christos <h2 id="national">National histories of legal time</h2>
    787  1.1  christos <dl>
    788  1.1  christos <dt>Australia</dt>
    789  1.6  christos <dd>The Parliamentary Library commissioned a <a
    790  1.1  christos href="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
    791  1.1  christos paper on daylight saving time in Australia</a>.
    792  1.1  christos The Bureau of Meteorology publishes a list of <a
    793  1.1  christos href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
    794  1.1  christos Dates of Daylight Savings Time within Australia</a>.</dd>
    795  1.1  christos <dt>Belgium</dt>
    796  1.1  christos <dd>The Royal Observatory of Belgium maintains a table of <a
    797  1.4  christos href="https://www.astro.oma.be/GENERAL/INFO/nli001a.html"
    798  1.1  christos hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
    799  1.1  christos <dt>Brazil</dt>
    800  1.1  christos <dd>The Time Service Department of the National Observatory
    801  1.1  christos records <a href="http://pcdsh01.on.br/DecHV.html"
    802  1.1  christos hreflang="pt-BR">Brazil's daylight saving time decrees (in
    803  1.1  christos Portuguese)</a>.</dd>
    804  1.1  christos <dt>Canada</dt>
    805  1.1  christos <dd>National Research Council Canada publishes current
    806  1.1  christos and some older information about <a
    807  1.6  christos href="https://nrc.canada.ca/en/certifications-evaluations-standards/canadas-official-time/time-zones-daylight-saving-time">time
    808  1.6  christos zones and daylight saving time</a>.</dd>
    809  1.1  christos <dt>Chile</dt>
    810  1.1  christos <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
    811  1.4  christos <a href="https://www.horaoficial.cl/historia_hora.html" hreflang="es">history of
    812  1.1  christos Chile's official time (in Spanish)</a>.</dd>
    813  1.3  christos <dt>China</dt>
    814  1.3  christos <dd>The Hong Kong Observatory maintains a
    815  1.3  christos <a href="https://www.hko.gov.hk/gts/time/Summertime.htm">history of
    816  1.3  christos  summer time in Hong Kong</a>,
    817  1.3  christos and Macau's Meteorological and Geophysical Bureau maintains a <a
    818  1.3  christos href="http://www.smg.gov.mo/smg/geophysics/e_t_Summer%20Time.htm">similar
    819  1.3  christos history for Macau</a>.
    820  1.3  christos Unfortunately the latter is incomplete and has errors.</dd>
    821  1.1  christos <dt>Czech Republic</dt>
    822  1.1  christos <dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
    823  1.1  christos hreflang="cs">When daylight saving time starts and ends (in Czech)</a>
    824  1.1  christos summarizes and cites historical DST regulations.</dd>
    825  1.1  christos <dt>Germany</dt>
    826  1.1  christos <dd>The National Institute for Science and Technology maintains the <a
    827  1.1  christos href="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
    828  1.1  christos of Legal Time in Germany</a>.</dd>
    829  1.1  christos <dt>Israel</dt>
    830  1.1  christos <dd>The Interior Ministry periodically issues <a
    831  1.1  christos href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
    832  1.1  christos hreflang="he">announcements (in Hebrew)</a>.</dd>
    833  1.1  christos <dt>Italy</dt>
    834  1.6  christos <dd>The National Institute of Metrological Research publishes a
    835  1.4  christos <a href="http://oldsite.inrim.it/res/tf/ora_legale_i.shtml" hreflang="it">table
    836  1.4  christos of civil time (in Italian)</a>.</dd>
    837  1.2  christos <dt>Malaysia</dt>
    838  1.2  christos <dd>See Singapore <a href="#Singapore">below</a>.</dd>
    839  1.1  christos <dt>Mexico</dt>
    840  1.1  christos <dd>The Investigation and Analysis Service of the Mexican Library of
    841  1.1  christos Congress has published a <a
    842  1.1  christos href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
    843  1.1  christos hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
    844  1.1  christos <dt>Netherlands</dt>
    845  1.1  christos <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
    846  1.1  christos hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
    847  1.1  christos covers the history of local time in the Netherlands from ancient times.</dd>
    848  1.1  christos <dt>New Zealand</dt>
    849  1.1  christos <dd>The Department of Internal Affairs maintains a brief <a
    850  1.1  christos href="https://www.dia.govt.nz/Daylight-Saving-History">History of
    851  1.6  christos Daylight Saving</a>.</dd>
    852  1.1  christos <dt>Singapore</dt>
    853  1.1  christos <dd><a id="Singapore"
    854  1.6  christos href="http://www.math.nus.edu.sg/~mathelmr/teaching/timezone.html">Why
    855  1.1  christos is Singapore in the "Wrong" Time Zone?</a> details the
    856  1.1  christos history of legal time in Singapore and Malaysia.</dd>
    857  1.1  christos <dt>United Kingdom</dt>
    858  1.1  christos <dd><a
    859  1.1  christos href="https://www.polyomino.org.uk/british-time/">History of
    860  1.1  christos legal time in Britain</a> discusses in detail the country
    861  1.6  christos with perhaps the best-documented history of clock adjustments.</dd>
    862  1.1  christos <dt>United States</dt>
    863  1.1  christos <dd>The Department of Transportation's <a
    864  1.1  christos href="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
    865  1.1  christos Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
    866  1.1  christos <dt>Uruguay</dt>
    867  1.1  christos <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
    868  1.1  christos Navy (SOHMA) publishes an annual <a
    869  1.6  christos href="http://www.armada.gub.uy/sohma/index.php/servicios/datos-astronomicos" hreflang="es">almanac
    870  1.1  christos (in Spanish)</a>.</dd>
    871  1.1  christos </dl>
    872  1.6  christos </section>
    873  1.6  christos 
    874  1.6  christos <section>
    875  1.1  christos <h2 id="precision">Precision timekeeping</h2>
    876  1.1  christos <ul>
    877  1.1  christos <li><a
    878  1.1  christos href="http://leapsecond.com/hpan/an1289.pdf">The
    879  1.1  christos Science of Timekeeping</a> is a thorough introduction
    880  1.1  christos to the theory and practice of precision timekeeping.</li>
    881  1.1  christos <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
    882  1.1  christos Time 2016</a> contains several freely-readable papers.</li>
    883  1.1  christos <li><a href="http://www.ntp.org"><abbr
    884  1.1  christos title="Network Time Protocol">NTP</abbr>: The Network
    885  1.1  christos Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
    886  1.1  christos discusses how to synchronize clocks of
    887  1.1  christos Internet hosts.</li>
    888  1.2  christos <li>The <a href="https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf"><span style="font-variant: small-caps">Huygens</span></a>
    889  1.2  christos family of software algorithms can achieve accuracy to a few tens of
    890  1.2  christos nanoseconds in scalable server farms without special hardware.</li>
    891  1.1  christos <li>The <a
    892  1.1  christos href="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
    893  1.1  christos Time Protocol</a> (<abbr
    894  1.1  christos title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
    895  1.2  christos can achieve submicrosecond clock accuracy on a local area network
    896  1.2  christos with special-purpose hardware.</li>
    897  1.1  christos <li><a
    898  1.1  christos href="https://tools.ietf.org/html/rfc4833">Timezone
    899  1.1  christos Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
    900  1.1  christos (Internet <abbr>RFC</abbr> 4833)
    901  1.1  christos specifies a <a
    902  1.1  christos href="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
    903  1.1  christos option for a server to configure
    904  1.1  christos a client's time zone and daylight saving settings automatically.</li>
    905  1.1  christos <li><a
    906  1.1  christos href="https://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
    907  1.1  christos Times</a> explains more abstruse astronomical time scales like
    908  1.1  christos <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
    909  1.1  christos <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
    910  1.1  christos <abbr title="Barycentric Dynamic Time">TDB</abbr>.
    911  1.1  christos <a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
    912  1.1  christos Scales</a> goes into more detail, particularly for historical variants.</li>
    913  1.1  christos <li>The <a href="https://www.iau.org"><abbr
    914  1.1  christos title="International Astronomical Union">IAU</abbr></a>'s <a
    915  1.1  christos href="http://www.iausofa.org"><abbr
    916  1.1  christos title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
    917  1.1  christos collection contains C and <a
    918  1.1  christos href="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
    919  1.1  christos code for converting among time scales like
    920  1.1  christos <abbr title="International Atomic Time">TAI</abbr>,
    921  1.1  christos <abbr>TDB</abbr>, <abbr>TDT</abbr> and
    922  1.1  christos <abbr>UTC</abbr>.</li>
    923  1.1  christos <li><a
    924  1.1  christos href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
    925  1.1  christos &ndash; Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
    926  1.1  christos diverse local time
    927  1.1  christos scales used by each landed mission on Mars.</li>
    928  1.1  christos <li><a href="http://leapsecond.com">LeapSecond.com</a> is
    929  1.1  christos dedicated not only to leap seconds but to precise time and frequency
    930  1.1  christos in general. It covers the state of the art in amateur timekeeping, and
    931  1.1  christos how the art has progressed over the past few decades.</li>
    932  1.1  christos <li><a
    933  1.1  christos href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
    934  1.1  christos title="International Earth Rotation and Reference Systems Service">IERS</abbr>
    935  1.1  christos Bulletins</a> contains official publications of the International
    936  1.1  christos Earth Rotation and Reference Systems Service, which decides when leap
    937  1.4  christos seconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds
    938  1.1  christos via an optional "<code>right</code>" configuration, as opposed to the
    939  1.1  christos default "<code>posix</code>" configuration.</li>
    940  1.1  christos <li><a href="https://developers.google.com/time/smear">Leap Smear</a>
    941  1.1  christos discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
    942  1.1  christos leap second so that they disagree with <abbr>UTC</abbr> by at most a
    943  1.1  christos half second, even though every <abbr>POSIX</abbr> minute has exactly
    944  1.4  christos sixty seconds. This approach works with the default <code><abbr>tz</abbr></code>
    945  1.1  christos "<code>posix</code>" configuration, is <a
    946  1.1  christos href="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
    947  1.1  christos the <abbr>NTP</abbr> reference implementation, and is used by major
    948  1.1  christos cloud service providers.</li>
    949  1.1  christos <li>The <a
    950  1.1  christos href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
    951  1.1  christos Second Discussion List</a> covers <a
    952  1.1  christos href="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
    953  1.1  christos and Klepczynski's 1999 proposal to discontinue leap seconds</a>,
    954  1.1  christos discussed further in
    955  1.1  christos <a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
    956  1.1  christos leap second: its history and possible future</a>.
    957  1.1  christos <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
    958  1.1  christos might be redefined
    959  1.1  christos without Leap Seconds</a> gives pointers on this
    960  1.1  christos contentious issue, which was active until 2015 and could become active
    961  1.1  christos again.</li>
    962  1.1  christos </ul>
    963  1.6  christos </section>
    964  1.6  christos 
    965  1.6  christos <section>
    966  1.1  christos <h2 id="notation">Time notation</h2>
    967  1.1  christos <ul>
    968  1.1  christos <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
    969  1.1  christos Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
    970  1.1  christos zone names, abbreviations, identifiers, and formats. For example, it
    971  1.1  christos contains French translations for "Eastern European Summer Time",
    972  1.1  christos "<abbr title="Eastern European Summer Time">EEST</abbr>", and
    973  1.1  christos "Bucharest". Its
    974  1.1  christos <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
    975  1.1  christos charts</a> show these values for many locales. Data values are available in
    976  1.1  christos both <abbr title="Locale Data Markup Language">LDML</abbr>
    977  1.1  christos (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
    978  1.1  christos <li>
    979  1.1  christos <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
    980  1.6  christos the international standard date and time notation</a> covers
    981  1.1  christos <a
    982  1.6  christos href="https://www.iso.org/standard/70907.html"><em><abbr
    983  1.6  christos title="International Organization for Standardization">ISO</abbr>
    984  1.6  christos 8601-1:2019 &ndash; Date and time &ndash; Representations for information
    985  1.6  christos interchange &ndash; Part 1: Basic rules</em></a>.</li>
    986  1.1  christos <li>
    987  1.6  christos <a href="https://www.w3.org/TR/xmlschema/#dateTime"><abbr>XML</abbr>
    988  1.1  christos Schema: Datatypes &ndash; dateTime</a> specifies a format inspired by
    989  1.1  christos <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
    990  1.1  christos <li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">&sect;3.3 of
    991  1.1  christos Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
    992  1.1  christos specifies the time notation used in email and <a
    993  1.1  christos href="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
    994  1.1  christos headers.</li>
    995  1.1  christos <li>
    996  1.1  christos <a href="https://tools.ietf.org/html/rfc3339">Date and Time
    997  1.1  christos on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
    998  1.1  christos specifies an <abbr>ISO</abbr> 8601
    999  1.1  christos profile for use in new Internet
   1000  1.1  christos protocols.</li>
   1001  1.1  christos <li>
   1002  1.1  christos <a href="https://www.hackcraft.net/web/datetime/">Date &amp; Time
   1003  1.1  christos Formats on the Web</a> surveys web- and Internet-oriented date and time
   1004  1.1  christos formats.</li>
   1005  1.1  christos <li>Alphabetic time zone abbreviations should not be used as unique
   1006  1.1  christos identifiers for <abbr>UT</abbr> offsets as they are ambiguous in
   1007  1.1  christos practice. For example, in English-speaking North America
   1008  1.1  christos "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
   1009  1.1  christos but in China it denotes 8 hours ahead of <abbr>UT</abbr>,
   1010  1.1  christos and French-speaking North Americans prefer
   1011  1.1  christos "<abbr title="Heure Normale du Centre">HNC</abbr>" to
   1012  1.1  christos "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
   1013  1.2  christos database contains English abbreviations for many timestamps;
   1014  1.1  christos unfortunately some of these abbreviations were merely the database maintainers'
   1015  1.1  christos inventions, and these have been removed when possible.</li>
   1016  1.1  christos <li>Numeric time zone abbreviations typically count hours east of
   1017  1.1  christos <abbr>UT</abbr>, e.g., +09 for Japan and
   1018  1.1  christos &minus;10 for Hawaii. However, the <abbr>POSIX</abbr>
   1019  1.1  christos <code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
   1020  1.1  christos For example, one might use <code><abbr>TZ</abbr>="<abbr
   1021  1.1  christos title="Japan Standard Time">JST</abbr>-9"</code> and
   1022  1.1  christos <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
   1023  1.1  christos for Japan and Hawaii, respectively. If the
   1024  1.1  christos <code><abbr>tz</abbr></code> database is available, it is usually better to use
   1025  1.1  christos settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
   1026  1.1  christos <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
   1027  1.2  christos confusion, handle old timestamps better, and insulate you better from
   1028  1.1  christos any future changes to the rules. One should never set
   1029  1.1  christos <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
   1030  1.1  christos <code>"GMT-9"</code>, though, since this would incorrectly imply that
   1031  1.1  christos local time is nine hours ahead of <abbr>UT</abbr> and the time zone
   1032  1.1  christos is called "<abbr>GMT</abbr>".</li>
   1033  1.1  christos </ul>
   1034  1.6  christos </section>
   1035  1.6  christos 
   1036  1.6  christos <section>
   1037  1.1  christos <h2 id="see-also">See also</h2>
   1038  1.1  christos <ul>
   1039  1.1  christos <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li>
   1040  1.1  christos <li><a href="tz-art.html">Time and the Arts</a></li>
   1041  1.1  christos </ul>
   1042  1.6  christos </section>
   1043  1.6  christos 
   1044  1.6  christos <footer>
   1045  1.1  christos <hr>
   1046  1.1  christos This web page is in the public domain, so clarified as of
   1047  1.1  christos 2009-05-17 by Arthur David Olson.
   1048  1.1  christos <br>
   1049  1.1  christos Please send corrections to this web page to the
   1050  1.1  christos <a href="mailto:tz (a] iana.org">time zone mailing list</a>.
   1051  1.6  christos </footer>
   1052  1.1  christos </body>
   1053  1.1  christos </html>
   1054