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      4 <title>Time zone and daylight saving time data</title>
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     11 <h1>Time zone and daylight saving time data</h1>
     12 <p>
     13 <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
     14 <a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
     15 rules are controlled by individual
     16 governments. They are sometimes changed with little notice, and their
     17 histories and planned futures are often recorded only fitfully. Here
     18 is a summary of attempts to organize and record relevant data in this
     19 area.
     20 </p>
     21   <h3>Outline</h3>
     22   <nav>
     23     <ul>
     24       <li>The <code><abbr>tz</abbr></code> database product and process
     25 	<ul>
     26 	  <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li>
     27 	  <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li>
     28 	  <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li>
     29 	  <li><a href="#coordinating">Coordinating with governments and distributors</a></li>
     30 	  <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li>
     31 	</ul>
     32       </li>
     33       <li>Uses of the <code><abbr>tz</abbr></code> database
     34 	<ul>
     35 	  <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li>
     36 	  <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li>
     37 	  <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li>
     38 	  <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li>
     39 	  <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li>
     40 	</ul>
     41       </li>
     42       <li>Related data
     43 	<ul>
     44 	  <li><a href="#other-dbs">Other time zone databases</a></li>
     45 	  <li><a href="#maps">Maps</a></li>
     46 	  <li><a href="#boundaries">Time zone boundaries</a></li>
     47 	</ul>
     48       </li>
     49       <li>Timekeeping concepts
     50 	<ul>
     51 	  <li><a href="#civil">Civil time concepts and history</a></li>
     52 	  <li><a href="#national">National histories of legal time</a></li>
     53 	  <li><a href="#costs">Costs and benefits of time shifts</a></li>
     54 	  <li><a href="#precision">Precision timekeeping</a></li>
     55 	  <li><a href="#notation">Time notation</a></li>
     56 	</ul>
     57       </li>
     58       <li><a href="#see-also">See also</a></li>
     59     </ul>
     60   </nav>
     61 
     62 <section>
     63 <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
     64 <p>
     65 The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
     66 time zone database contains code and data
     67 that represent the history of local time
     68 for many representative locations around the globe.
     69 It is updated periodically to reflect changes made by political bodies
     70 to time zone boundaries and daylight saving rules.
     71 This database (known as <code><abbr>tz</abbr></code>,
     72 <code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)
     73 is used by several implementations,
     74 including
     75 <a href="https://www.gnu.org/software/libc/">the
     76 <abbr title="GNU's Not Unix">GNU</abbr>
     77 C Library</a> (used in
     78 <a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),
     79 <a href="https://www.android.com">Android</a>,
     80 <a href="https://www.freebsd.org">Free<abbr
     81 title="Berkeley Software Distribution">BSD</abbr></a>,
     82 <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
     83 <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
     84 <a href="https://www.chromium.org/chromium-os/">Chromium OS</a>,
     85 <a href="https://cygwin.com">Cygwin</a>,
     86 <a href="https://mariadb.org">MariaDB</a>,
     87 <a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
     88 <a href="https://www.mysql.com">MySQL</a>,
     89 <a href="https://en.wikipedia.org/wiki/WebOS"><abbr
     90 title="Web Operating System">webOS</abbr></a>,
     91 <a href="https://en.wikipedia.org/wiki/IBM_AIX"><abbr
     92 title="Advanced Interactive eXecutive">AIX</abbr></a>,
     93 <a href="https://www.apple.com/ios"><abbr
     94 title="iPhone OS">iOS</abbr></a>,
     95 <a href="https://www.apple.com/macos">macOS</a>,
     96 <a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,
     97 <a href="https://www.vmssoftware.com">Open<abbr
     98 title="Virtual Memory System">VMS</abbr></a>,
     99 <a href="https://www.oracle.com/database/">Oracle Database</a>, and
    100 <a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>
    101 <p>
    102 Each main entry in the database represents a <dfn>timezone</dfn>
    103 for a set of civil-time clocks that have all agreed since 1970.
    104 Timezones are typically identified by continent or ocean and then by the
    105 name of the largest city within the region containing the clocks.
    106 For example, <code>America/New_York</code>
    107 represents most of the <abbr title="United States">US</abbr> eastern time zone;
    108 <code>America/Phoenix</code> represents most of Arizona, which
    109 uses mountain time without daylight saving time (<abbr>DST</abbr>);
    110 <code>America/Detroit</code> represents most of Michigan, which uses
    111 eastern time but with different <abbr>DST</abbr> rules in 1975;
    112 and other entries represent smaller regions like Starke County,
    113 Indiana, which switched from central to eastern time in 1991
    114 and switched back in 2006.
    115 To use the database on an extended <a
    116 href="https://en.wikipedia.org/wiki/POSIX"><abbr
    117 title="Portable Operating System Interface">POSIX</abbr></a>
    118 implementation set the <code><abbr>TZ</abbr></code>
    119 environment variable to the location's full name,
    120 e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p>
    121 <p>
    122 Associated with each timezone is a history of offsets from
    123 <a href="https://en.wikipedia.org/wiki/Universal_Time">Universal
    124 Time</a> (<abbr>UT</abbr>), which is <a
    125 href="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean
    126 Time</a> (<abbr>GMT</abbr>) with days beginning at midnight;
    127 for timestamps after 1960 this is more precisely <a
    128 href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated
    129 Universal Time</a> (<abbr>UTC</abbr>).
    130 The database also records when daylight saving time was in use,
    131 along with some time zone abbreviations such as <abbr>EST</abbr>
    132 for Eastern Standard Time in the <abbr>US</abbr>.</p>
    133 </section>
    134 
    135 <section>
    136 <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>
    137 <p>
    138 The following <a
    139 href="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download
    140 the latest release's two
    141 <a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a>
    142 to a <abbr>GNU</abbr>/Linux or similar host.</p>
    143 <pre><code>mkdir tzdb
    144 cd tzdb
    145 <a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
    146 wget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
    147 <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 -
    148 gzip -dc tzdata-latest.tar.gz | tar -xf -
    149 </code></pre>
    150 <p>Alternatively, the following shell commands download the same
    151 release in a single-tarball format containing extra data
    152 useful for regression testing:</p>
    153 <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>
    154 <a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -
    155 </code></pre>
    156 <p>These commands use convenience links to the latest release
    157 of the <code><abbr>tz</abbr></code> database hosted by the
    158 <a href="https://www.iana.org/time-zones">Time Zone Database website</a>
    159 of the <a href="https://www.iana.org">Internet Assigned Numbers
    160 Authority (IANA)</a>.
    161 Older releases are in files named
    162 <code>tzcode<var>V</var>.tar.gz</code>,
    163 <code>tzdata<var>V</var>.tar.gz</code>, and
    164 <code>tzdb-<var>V</var>.tar.lz</code>,
    165 where <code><var>V</var></code> is the version.
    166 Since 1996, each version has been a four-digit year followed by
    167 lower-case letter (<samp>a</samp> through <samp>z</samp>,
    168 then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>
    169 through <samp>zzz</samp>, and so on).
    170 Since version 2022a, each release has been distributed in
    171 <a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06">POSIX
    172 ustar interchange format</a>, compressed as described above;
    173 older releases use a nearly compatible format.
    174 Since version 2016h, each release has contained a text file named
    175 "<samp>version</samp>" whose first (and currently only) line is the version.
    176 Older releases are <a href="https://ftp.iana.org/tz/releases/">archived</a>,
    177 and are also available in an
    178 <a href="ftp://ftp.iana.org/tz/releases/"><abbr
    179 title="File Transfer Protocol">FTP</abbr> directory</a> via a
    180 less secure protocol.</p>
    181 <p>Alternatively, a development repository of code and data can be
    182 retrieved from <a href="https://github.com">GitHub</a> via the shell
    183 command:</p>
    184 <pre><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a>
    185 </code></pre>
    186 <p>
    187 Since version 2012e, each release has been tagged in development repositories.
    188 Untagged commits are less well tested and probably contain
    189 more errors.</p>
    190 <p>
    191 After obtaining the code and data files, see the
    192 <code>README</code> file for what to do next.
    193 The code lets you compile the <code><abbr>tz</abbr></code> source files into
    194 machine-readable binary files, one for each location. The binary files
    195 are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>)
    196 specified by <a href="https://datatracker.ietf.org/doc/html/8536">Internet
    197 <abbr>RFC</abbr> 8536</a>.
    198 The code also lets
    199 you read a <abbr>TZif</abbr> file and interpret timestamps for that
    200 location.</p>
    201 </section>
    202 
    203 <section>
    204 <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
    205 <p>
    206 The <code><abbr>tz</abbr></code> code and data
    207 are by no means authoritative. If you find errors, please
    208 send changes to <a href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a>,
    209 the time zone mailing list. You can also <a
    210 href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
    211 and browse the <a
    212 href="https://mm.icann.org/pipermail/tz/">archive of old
    213 messages</a>.
    214 <a href="https://tzdata-meta.timtimeonline.com/">Metadata for mailing list
    215 discussions</a> and corresponding data changes can be
    216 generated <a href="https://github.com/timparenti/tzdata-meta">automatically</a>.
    217 </p>
    218 <p>
    219 Changes to the <code><abbr>tz</abbr></code> code and data are often
    220 propagated to clients via operating system updates, so
    221 client <code><abbr>tz</abbr></code> data can often be corrected by
    222 applying these updates. With GNU/Linux and similar systems, if your
    223 maintenance provider has not yet adopted the
    224 latest <code><abbr>tz</abbr></code> data, you can often short-circuit
    225 the process by tailoring the generic instructions in
    226 the <code><abbr>tz</abbr> README</code> file and installing the latest
    227 data yourself. System-specific instructions for installing the
    228 latest <code><abbr>tz</abbr></code> data have also been published
    229 for <a href="https://developer.ibm.com/articles/au-aix-olson-time-zone/"><abbr>AIX</abbr></a>,
    230 <a
    231 href="https://source.android.com/devices/tech/config/timezone-rules">Android</a>,
    232 <a
    233 href="https://unicode-org.github.io/icu/userguide/datetime/timezone/"><abbr
    234 title="International Components for Unicode">ICU</abbr></a>,
    235 <a href="https://www.ibm.com/support/pages/java-sdk-time-zone-update-utility"><abbr>IBM</abbr>
    236 JDK</a>,
    237 <a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
    238 href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
    239 <a href="https://nodatime.org/userguide/tzdb">Noda Time</a>, and <a
    240 href="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">OpenJDK/Oracle JDK</a>.
    241 </p>
    242 <p>Since version 2013a,
    243 sources for the <code><abbr>tz</abbr></code> database have been
    244 <a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
    245 title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
    246 <a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
    247 with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
    248 title="linefeed">LF</abbr></a>,
    249 which can be modified by common text editors such
    250 as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
    251 <a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
    252 <a href="https://www.vim.org">vim</a>.
    253 Specialized source-file editing can be done via the
    254 <a href="https://packagecontrol.io/packages/zoneinfo">Sublime
    255 zoneinfo</a> package for <a
    256 href="https://www.sublimetext.com">Sublime Text</a> and the <a
    257 href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
    258 zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
    259 Studio Code</a>.
    260 </p>
    261 <p>
    262 For further information about updates, please see
    263 <a href="https://datatracker.ietf.org/doc/html/rfc6557">Procedures for
    264 Maintaining the Time Zone Database</a> (Internet <abbr
    265 title="Request For Comments">RFC</abbr> 6557). More detail can be
    266 found in <a href="theory.html">Theory and pragmatics of the
    267 <code><abbr>tz</abbr></code> code and data</a>.
    268 <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
    269 displays changes between recent <code><abbr>tzdb</abbr></code> versions.
    270 </p>
    271 </section>
    272 
    273 <section>
    274 <h2 id="coordinating">Coordinating with governments and distributors</h2>
    275 <p>
    276 As discussed in
    277 "<a href="https://www.icann.org/en/blogs/details/how-time-zones-are-coordinated-13-03-2023-en">How
    278 Time Zones Are Coordinated</a>", the time zone database relies on
    279 collaboration among governments, the time zone database volunteer
    280 community, and data distributors downstream.
    281 <p>
    282 If your government plans to change its time zone boundaries or
    283 daylight saving rules, please send email to <a
    284 href="mailto:tz (a] iana.org"><code>tz (a] iana.org</code></a> well in advance,
    285 as this will lessen confusion and will coordinate updates to many cell phones,
    286 computers, and other devices around the world.
    287 In your email, please cite the legislation or regulation that specifies
    288 the change, so that it can be checked for details such as the exact times
    289 when clock transitions occur.
    290 It is OK if a rule change is planned to affect clocks
    291 far into the future, as a long-planned change can easily be reverted
    292 or otherwise altered with a year's notice before the change would have
    293 affected clocks.</p>
    294 <p>
    295 There is no fixed schedule for <code><abbr>tzdb</abbr></code> releases.
    296 However, typically a release occurs every few months.
    297 Many downstream timezone data distributors wait for
    298 a <code><abbr>tzdb</abbr></code> release before they produce an update
    299 to time zone behavior in consumer devices and software products.
    300 After a release, various parties must integrate, test,
    301 and roll out an update before <a
    302 href="https://en.wikipedia.org/wiki/End_user">end users</a> see changes.
    303 These updates can be expensive, for both the <a
    304 href="https://en.wikipedia.org/wiki/Quality_assurance">quality
    305 assurance</a> process and the overall cost of shipping and installing
    306 updates to each device's copy of <code><abbr>tzdb</abbr></code>.
    307 Updates may be batched with other updates and may take substantial
    308 time to reach end users after a release.
    309 Older devices may no longer be supported and thus may never be updated,
    310 which means they will continue to use out-of-date rules.</p>
    311 <p>
    312 For these reasons any rule change should be promulgated at least a
    313 year before it affects how clocks operate; otherwise, there is a good
    314 chance that many clocks will be wrong due to delays in propagating updates,
    315 and that residents will be confused or even actively resist the change.
    316 The shorter the notice, the more likely clock problems will arise; see "<a
    317 href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
    318 the Timing of Time Zone Changes</a>" for examples.
    319 </p>
    320 </section>
    321 
    322 <section>
    323 <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
    324 <ul>
    325 <li>The article
    326 <a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
    327 an encyclopedic summary.</li>
    328 <li><a href="tz-how-to.html">How to Read the
    329 tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
    330 database format.</li>
    331 <li><a
    332 href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
    333 literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
    334 database's style.</li>
    335 <li><a href="https://doi.org/10.1145/3340301.3341125">What time is it:
    336 managing time in the internet</a> analyzes the database longitudinally.</li>
    337 </ul>
    338 </section>
    339 
    340 <section>
    341 <h2 id="web">Web sites using recent versions of the
    342 <code><abbr>tz</abbr></code> database</h2>
    343 <p>
    344 These are listed roughly in ascending order of complexity and fanciness.
    345 </p>
    346 <ul>
    347 <li><a href="https://time.is">Time.is</a> shows locations'
    348 time and zones.</li>
    349 <li><a href="https://www.timejones.com">TimeJones.com</a>,
    350 <a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
    351 <a href="https://www.worldclock.com">The World Clock</a>
    352 are time zone converters.</li>
    353 <li><a href="https://timezonedb.com/download">TimeZoneDB Database</a>
    354 publishes <code><abbr>tzdb</abbr></code>-derived data in
    355 <a href="https://en.wikipedia.org/wiki/Comma-separated_values"><abbr
    356 title="comma-separated values">CSV</abbr></a> and
    357 in <a href="https://en.wikipedia.org/wiki/SQL"><abbr
    358 title="Structured Query Language">SQL</abbr></a> form.</li>
    359 <li><a
    360 href="https://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
    361 lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
    362 <li><a
    363 href="https://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
    364 Time in 1000 Places</a> uses descriptions of the values.</li>
    365 <li><a href="https://home.kpn.nl/vanadovv/time/TZworld.html">Complete
    366 timezone information for all countries</a>
    367 displays tables of <abbr>DST</abbr> rules.
    368 <li><a href="https://www.timeanddate.com/worldclock/">The World Clock &ndash;
    369 Worldwide</a> lets you sort zone names and convert times.</li>
    370 <li><a href="https://24timezones.com">24TimeZones</a> has a world
    371 time map and a time converter.</li>
    372 <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
    373 calculates the current time difference between locations.</li>
    374 <li><a href="https://www.wx-now.com">Weather Now</a> and
    375 <a href="https://www.thetimenow.com">The Time Now</a> list the weather too.</li>
    376 </ul>
    377 </section>
    378 
    379 <section>
    380 <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
    381 <ul>
    382 <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
    383 <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
    384 Distribution Service (tzdist) working group</a> defined <a
    385 href="https://datatracker.ietf.org/doc/html/rfc7808">TZDIST</a>
    386 (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
    387 along with <a href="https://datatracker.ietf.org/doc/html/rfc7809">CalDAV</a>
    388 (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
    389 transferring time zone data by reference.
    390 <a href="https://devguide.calconnect.org/Time-Zones/TZDS/">TZDIST
    391 implementations</a> are available.
    392 The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
    393 mailing list</a> discusses possible extensions.</li>
    394 <li>The <a href="https://datatracker.ietf.org/doc/html/rfc5545">
    395 Internet Calendaring and Scheduling Core Object Specification
    396 (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
    397 covers time zone
    398 data; see its VTIMEZONE calendar component.
    399 The iCalendar format requires specialized parsers and generators; a
    400 variant <a href="https://datatracker.ietf.org/doc/html/rfc6321">xCal</a>
    401 (Internet <abbr>RFC</abbr> 6321) uses
    402 <a href="https://www.w3.org/XML/"><abbr
    403 title="Extensible Markup Language">XML</abbr></a> format, and a variant
    404 <a href="https://datatracker.ietf.org/doc/html/rfc7265">jCal</a>
    405 (Internet <abbr>RFC</abbr> 7265)
    406 uses <a href="https://www.json.org"><abbr
    407 title="JavaScript Object Notation">JSON</abbr></a> format.</li>
    408 </ul>
    409 </section>
    410 
    411 <section>
    412 <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
    413 <p>Although some of these do not fully support
    414 <code><abbr>tz</abbr></code> data, in recent <code><abbr>tzdb</abbr></code>
    415 distributions you can generally work around compatibility problems by
    416 running the command <code>make rearguard_tarballs</code> and compiling
    417 from the resulting tarballs instead.</p>
    418 <ul>
    419 <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
    420 href="https://en.wikipedia.org/wiki/C_(programming_language)">C</a>
    421 program that compiles
    422 <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
    423 Vzic is freely
    424 available under the <a
    425 href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
    426 General Public License (<abbr
    427 title="General Public License">GPL</abbr>)</a>.</li>
    428 <li><a href="https://sourceforge.net/projects/tzical/">tziCal &ndash; tz
    429 database conversion utility</a> is like Vzic, except for the <a
    430 href="https://dotnet.microsoft.com">.NET framework</a>
    431 and with a <abbr>BSD</abbr>-style license.</li>
    432 <li><a
    433 href="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>
    434 contains a script <code>parse_olson</code> that compiles
    435 <code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
    436 modules. It is part of the Perl <a
    437 href="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>,
    438 which is freely
    439 available under both the <abbr>GPL</abbr> and the Perl Artistic
    440 License. DateTime::TimeZone also contains a script
    441 <code>tests_from_zdump</code> that generates test cases for each clock
    442 transition in the <code><abbr>tz</abbr></code> database.</li>
    443 <li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
    444 Database Parser</a> is a
    445 <a href="https://en.wikipedia.org/wiki/C++">C++</a> parser and
    446 runtime library with <a
    447 href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0355r7.html">API</a>
    448 adopted by
    449 <a href="https://en.wikipedia.org/wiki/C++20">C++20</a>,
    450 the current iteration of the C++ standard.
    451 It is freely available under the
    452 <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
    453 <li><a id="ICU" href="https://icu.unicode.org">International Components for
    454 Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
    455 href="https://en.wikipedia.org/wiki/Java_(programming_language)">Java</a>
    456 libraries for internationalization that
    457 has a compiler from <code><abbr>tz</abbr></code> source
    458 and from <abbr title="Common Locale Data Repository">CLDR</abbr> data
    459 (mentioned <a href="#CLDR">below</a>)
    460 into an <abbr>ICU</abbr>-specific format.
    461 <abbr>ICU</abbr> is freely available under a
    462 <abbr>BSD</abbr>-style license.</li>
    463 <li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
    464 the <a href="https://elixir-lang.org">Elixir</a> language downloads
    465 and compiles <code><abbr>tz</abbr></code> source and exposes <abbr
    466 title="Application Program Interface">API</abbr>s for use. It is
    467 freely available under the <abbr>MIT</abbr> license.</li>
    468 <li>Java-based compilers and libraries include:
    469 <ul>
    470 <li>The <a
    471 href="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">TZUpdater
    472 tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
    473 <a href="https://openjdk.java.net/">OpenJDK</a> and
    474 <a href="https://jdk.java.net/">Oracle JDK</a>.
    475 Although its source code is proprietary, its executable is available under the
    476 <a href="https://www.oracle.com/a/tech/docs/tzupdater-lic.html">Java SE
    477 Timezone Updater License Agreement</a>.</li>
    478 <li>The <a
    479 href="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
    480 SE 8 Date and Time</a> <abbr>API</abbr> can be supplemented by <a
    481 href="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
    482 which is freely available under a <abbr>BSD</abbr>-style license.</li>
    483 <li><a href="https://www.joda.org/joda-time/">Joda-Time &ndash; Java date
    484 and time <abbr>API</abbr></a> contains a class
    485 <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
    486 <code><abbr>tz</abbr></code> source into a binary format. It inspired
    487 Java 8 <code>java.time</code>, which its users should migrate to once
    488 they can assume Java 8 or later. It is available under the <a
    489 href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
    490 <li><a href="https://bell-sw.com/pages/iana-updater/">IANA Updater</a> and <a
    491 href="https://www.azul.com/products/open-source-tools/ziupdater-time-zone-tool/">ZIUpdater</a>
    492 are alternatives to TZUpdater. IANA Updater's license is unclear;
    493 ZIUpdater is licensed under the <abbr>GPL</abbr>.</li>
    494 <li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and
    495 time library for Android</a> and
    496 <a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date,
    497 time and interval library for Java</a> compile
    498 <code><abbr>tz</abbr></code> source into a binary format.
    499 Time4A is available under the Apache License and Time4J is
    500 available under the <a
    501 href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
    502 General Public License (<abbr title="Lesser General Public
    503 License">LGPL</abbr>)</a>.</li>
    504 <li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
    505 Java-based libraries.</li>
    506 </ul>
    507 <li><a href="https://nodatime.org">Noda Time &ndash; Date and
    508 time <abbr>API</abbr> for .NET</a>
    509 is like Joda-Time and Time4J, but for the .NET framework instead of Java.
    510 It is freely available under the Apache License.</li>
    511 <li>Many modern
    512 <a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>
    513 runtimes support <code><abbr>tz</abbr></code> natively via the
    514 <samp>timeZone</samp> option of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat"><samp>Intl.DateTimeFormat</samp></a>.
    515 This can be used as-is or with most of the following libraries,
    516 many of which also support runtimes lacking the <samp>timeZone</samp> option.
    517 <ul>
    518 <li>The <a
    519 href="https://github.com/formatjs/date-time-format-timezone"><samp>Intl.DateTimeFormat</samp>
    520 timezone polyfill</a>
    521 is freely available under a <abbr>BSD</abbr>-style license.</li>
    522 <li>The <a href="https://date-fns.org/">date-fns</a>
    523 library manipulates timezone-aware timestamps in browsers and
    524 in <a href="https://nodejs.org/en/">Node.js</a>.
    525 It is freely available under the <abbr>MIT</abbr> license.</li>
    526 <li><a href="https://github.com/iamkun/dayjs">Day.js</a> is a
    527 minimalist replacement for the date and time API of
    528 the <a href="https://momentjs.com/docs/">now-legacy Moment.js</a> date
    529 manipulation library.
    530 It is freely available under the <abbr>MIT</abbr> license.</li>
    531 <li><a href="https://moment.github.io/luxon/">Luxon</a> improves
    532 timezone support for the <samp>Intl</samp> API.
    533 It is freely available under the <abbr>MIT</abbr> license.</li>
    534 <li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
    535 Moment.js plugin.
    536 It is freely available under the <abbr>MIT</abbr> license.</li>
    537 <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
    538 JavaScript library that supports date arithmetic that is time zone
    539 aware. It is freely available under the <abbr>MIT</abbr> license.</li>
    540 <li><a href="https://www.npmjs.com/package/@tubular/time">@tubular/time</a>
    541 supports live <code><abbr>tzdb</abbr></code> updates,
    542 astronomical and atomic time, a command-line interface,
    543 and full <a
    544 href="https://en.wikipedia.org/wiki/TypeScript">TypeScript</a>.
    545 Its companion <a
    546 href="https://www.npmjs.com/package/@tubular/time-tzdb">@tubular/time-tzdb</a>
    547 can generate <abbr>TZif</abbr> and other files, and a companion website
    548 <a href="https://tzexplorer.org">Timezone Database Explorer</a> lets you
    549 convert timestamps, view transition histories, and download code and data.
    550 It is freely available under the <abbr>MIT</abbr> license.</li>
    551 </ul>
    552 The proposed <a
    553 href="https://github.com/tc39/proposal-temporal"><samp>Temporal</samp>
    554 objects</a> let programs access an abstract view of
    555 <code><abbr>tzdb</abbr></code> data, and are designed to replace <a
    556 href="https://codeofmatt.com/javascript-date-type-is-horribly-broken/">JavaScript's
    557 problematic <samp>Date</samp> objects</a> when working with dates and times.
    558 <li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
    559 compiler from <code><abbr>tz</abbr></code> source into
    560 <a href="https://julialang.org/">Julia</a>. It is freely available
    561 under the <abbr>MIT</abbr> license.</li>
    562 <li><a href="https://github.com/pavkam/tzdb"><abbr>TZDB</abbr> &ndash;
    563 <abbr>IANA</abbr> Time Zone Database for Delphi/<abbr
    564 title="Free Pascal Compiler">FPC</abbr></a>
    565 compiles from <code><abbr>tz</abbr></code> source into
    566 <a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>
    567 as compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>
    568 and <a
    569 href="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.
    570 It is freely available under a <abbr>BSD</abbr>-style license.</li>
    571 <li><a href="http://pytz.sourceforge.net">pytz &ndash; World Timezone
    572 Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
    573 <a href="https://www.python.org">Python</a>.
    574 It is freely available under a <abbr>BSD</abbr>-style license.
    575 In code that can assume Python 3.6 or later it is largely superseded; see <a
    576 href="https://blog.ganssle.io/articles/2018/03/pytz-fastest-footgun.html">pytz:
    577 The Fastest Footgun in the West</a>.</li>
    578 <li><a href="https://tzinfo.github.io">TZInfo &ndash;
    579 Ruby Timezone Library</a>
    580 compiles <code><abbr>tz</abbr></code> source into
    581 <a href="https://www.ruby-lang.org/en/">Ruby</a>.
    582 It is freely available under the <abbr>MIT</abbr> license.</li>
    583 <li>The <a href="https://www.squeaksource.com/Chronos/">Chronos Date/Time
    584 Library</a> is
    585 a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
    586 library that compiles <code><abbr>tz</abbr></code> source into a time
    587 zone repository whose format
    588 is either proprietary or an <abbr>XML</abbr>-encoded
    589 representation.</li>
    590 <li><a id="Tcl" href="https://tcl.tk">Tcl</a>
    591 contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
    592 source into text files, along with a runtime that can read those
    593 files. Tcl is freely available under a <abbr>BSD</abbr>-style
    594 license.</li>
    595 </ul>
    596 </section>
    597 
    598 <section>
    599 <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
    600 <ul>
    601 <li>The <a
    602 href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
    603 Library</a>
    604 has an independent, thread-safe implementation of
    605 a <abbr>TZif</abbr> file reader.
    606 This library is freely available under the LGPL
    607 and is widely used in <abbr>GNU</abbr>/Linux systems.</li>
    608 <li><a href="https://www.gnome.org">GNOME</a>'s
    609 <a href="https://developer.gnome.org/glib/">GLib</a> has
    610 a <abbr>TZif</abbr> file reader written in C that
    611 creates a <code>GTimeZone</code> object representing sets
    612 of <abbr>UT</abbr> offsets.
    613 It is freely available under the <abbr>LGPL</abbr>.</li>
    614 <li>The
    615 <a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
    616 <code>baltzo::TimeZoneUtil</code> component contains a C++
    617 implementation of a <abbr>TZif</abbr> file reader. It is freely available under
    618 the Apache License.</li>
    619 <li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
    620 library that translates between <abbr>UT</abbr> and civil time and
    621 can read <abbr>TZif</abbr> files. It is freely available under the Apache
    622 License.</li>
    623 <li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
    624 library that reads <abbr>TZif</abbr> files and converts
    625 timestamps from one time zone or format to another.
    626 It is used by <a href="https://secure.php.net"><abbr
    627 title="PHP: Hypertext Preprocessor">PHP</abbr></a>,
    628 <a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
    629 and <a href="https://www.mongodb.com">MongoDB</a>.
    630 It is freely available under the <abbr>MIT</abbr> license.</li>
    631 <li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
    632 <abbr>TZif</abbr> file reader.</li>
    633 <li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile">
    634 DateTime::TimeZone::Tzfile</a>
    635 is a <abbr>TZif</abbr> file reader written in Perl.
    636 It is freely available under the same terms as Perl
    637 (dual <abbr>GPL</abbr> and Artistic license).</li>
    638 <li>Python has a <a id="python-zoneinfo"
    639 href="https://docs.python.org/3/library/zoneinfo.html"><code>zoneinfo.ZoneInfo</code>
    640 class</a> that reads <abbr>TZif</abbr> data and creates objects
    641 that represent <code><abbr>tzdb</abbr></code> timezones.
    642 Python is freely available under the
    643 <a href="https://docs.python.org/3/license.html">Python Software Foundation
    644 License</a>.
    645 A companion <a id="pypi-tzdata" href="https://pypi.org/">PyPI</a> module
    646 <a href="https://pypi.org/project/tzdata/"><code>tzdata</code></a>
    647 supplies TZif data if the underlying system data cannot be found;
    648 it is freely available under the Apache License.</li>
    649 <li>The
    650 public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
    651 library contains a Python tool that
    652 converts <abbr>TZif</abbr> data into
    653 <abbr>JSON</abbr>-format data suitable for use
    654 in its JavaScript library for time zone conversion. Dates before 1970
    655 are not supported.</li>
    656 <li>The <a
    657 href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
    658 package contains <a href="https://www.haskell.org">Haskell</a> code that
    659 parses and uses <abbr>TZif</abbr> data. It is freely
    660 available under a <abbr>BSD</abbr>-style license.</li>
    661 </ul>
    662 </section>
    663 
    664 <section>
    665 <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
    666 <ul>
    667 <li><a href="https://foxclocks.org">FoxClocks</a>
    668 is an extension for <a href="https://www.google.com/chrome/">Google
    669 Chrome</a> and for <a
    670 href="https://wiki.mozilla.org/Modules/Toolkit">Mozilla
    671 Toolkit</a> applications like <a
    672 href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
    673 href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
    674 It displays multiple clocks in the application window, and has a mapping
    675 interface to <a href="https://www.google.com/earth/">Google Earth</a>.
    676 It is freely available under the <abbr>GPL</abbr>.</li>
    677 <li><a href="https://golang.org">Go programming language</a>
    678 implementations contain a copy of a 32-bit subset of a recent
    679 <code><abbr>tz</abbr></code> database in a
    680 Go-specific format.</li>
    681 <li>Microsoft Windows 8.1
    682 and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
    683 data (mentioned <a href="#CLDR">below</a>) used by the
    684 <a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /
    685 <a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes
    686 <a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and
    687 <a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.
    688 <a id="System.TimeZoneInfo"
    689 href="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
    690 Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes
    691 the older, proprietary method of Microsoft Windows 2000 and later,
    692 which stores time zone data in the
    693 <a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
    694 <a
    695 href="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone &rarr;
    696 Tzid table</a> or <a
    697 href="https://github.com/unicode-org/cldr/blob/master/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
    698 file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
    699 to <code><abbr>tz</abbr></code> names.
    700 These mappings can be performed programmatically via the <a href="https://github.com/mj1856/TimeZoneConverter">TimeZoneConverter</a> .NET library,
    701 or the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.
    702 <li><a
    703 href="https://www.oracle.com/java/index.html">Oracle
    704 Java</a> contains a copy of a subset of a recent
    705 <code><abbr>tz</abbr></code> database in a
    706 Java-specific format.</li>
    707 </ul>
    708 </section>
    709 
    710 <section>
    711 <h2 id="other-dbs">Other time zone databases</h2>
    712 <ul>
    713 <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
    714 is Astrodienst's Web version of Shanks and Pottenger's out-of-print
    715 time zone history atlases
    716 <a href="https://www.worldcat.org/oclc/468828649">for the US</a> and
    717 <a href="https://www.worldcat.org/oclc/76950459">for the world</a>.
    718 Although these extensive atlases
    719 <a href="https://astrologynewsservice.com/opinion/how-astrologers-contributed-to-the-information-age-a-brief-history-of-time/">were
    720 sources for much of the older <code><abbr>tz</abbr></code> data</a>,
    721 they are unreliable as Shanks appears to have
    722 guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
    723 sources and do not indicate which entries are guesswork.</li>
    724 <li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
    725 its own <code>tztab</code>(4) format.</li>
    726 <li>Microsoft Windows has proprietary data mentioned
    727 <a href="#System.TimeZoneInfo">above</a>.</li>
    728 <li><a href="https://www.worldtimeserver.com">World Time Server</a>
    729 is another time zone database.</li>
    730 <li>The <a
    731 href="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
    732 Schedules Information Manual</a> of the
    733 International Air Transport Association
    734 gives current time zone rules for airports served by commercial aviation.</li>
    735 </ul>
    736 </section>
    737 
    738 <section>
    739 <h2 id="maps">Maps</h2>
    740 <ul>
    741 <li>The <a
    742 href="https://www.cia.gov/the-world-factbook/maps/world-regional/">World
    743 and Regional Maps section</a> of <em>The World Factbook</em>, published by the
    744 <a href="https://www.cia.gov">US Central Intelligence
    745 Agency (<abbr
    746 title="Central Intelligence Agency">CIA</abbr>)</a>, contains a time
    747 zone map; the
    748 <a
    749 href="https://legacy.lib.utexas.edu/maps/world.html">Perry&ndash;Casta&ntilde;eda
    750 Library Map Collection</a>
    751 of the University of Texas at Austin has copies of
    752 recent editions.
    753 The pictorial quality is good,
    754 but the maps do not indicate daylight saving time,
    755 and parts of the data are a few years out of date.</li>
    756 <li><a href="https://www.worldtimezone.com">World Time Zone Map
    757 with current time</a>
    758 has several fancy time zone maps; it covers Russia particularly well.
    759 The maps' pictorial quality is not quite as good as the
    760 <abbr>CIA</abbr>'s
    761 but the maps are more up to date.</li>
    762 <li><a
    763 href="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
    764 much is time wrong around the world?</a> maps the difference between
    765 mean solar and standard time, highlighting areas such as western China
    766 where the two differ greatly. It's a bit out of date, unfortunately.</li>
    767 </ul>
    768 </section>
    769 
    770 <section>
    771 <h2 id="boundaries">Time zone boundaries</h2>
    772 <p>Geographical boundaries between timezones are available
    773 from several <a
    774 href="https://en.wikipedia.org/wiki/Internet_geolocation">Internet
    775 geolocation</a>
    776 services and other sources.</p>
    777 <ul>
    778 <li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
    779 Boundary Builder</a> extracts
    780 <a href="https://www.openstreetmap.org">Open Street Map</a> data to build
    781 boundaries of <code><abbr>tzdb</abbr></code> timezones.
    782 Its code is freely available under the <abbr>MIT</abbr> license, and
    783 its data entries are freely available under the
    784 <a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
    785 Open Database License</a>. The maps' borders appear to be quite accurate.</li>
    786 <li>Programmatic interfaces that map geographical coordinates via tz_world to
    787 <code><abbr>tzdb</abbr></code> timezones include:
    788 <ul>
    789 <li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
    790 written in <a
    791 href="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
    792 and is freely available under the <abbr>MIT</abbr> license.</li>
    793 <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
    794 is written in Go and is freely available under the Apache License.</li>
    795 <li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
    796 in both Java and
    797 <a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
    798 form, is freely available under the MIT license.</li>
    799 <li>For Node.js,
    800 the <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
    801 is freely available under the MIT license, and
    802 the <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
    803 is in the public domain.</li>
    804 <li>The <a
    805 href="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
    806 library for Python is freely available under the MIT license.
    807 <li>The <a
    808 href="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
    809 library for Ruby is freely available under the MIT license.</li>
    810 </ul></li>
    811 <li>Free access via a network API, if you register a key, is provided by
    812 the <a
    813 href="https://www.geonames.org/export/web-services.html#timezone">GeoNames
    814 Timezone web service</a>, the <a
    815 href="https://developers.google.com/maps/documentation/timezone/intro">Google
    816 Maps Time Zone API</a>, and
    817 the <a href="https://timezonedb.com/api">TimeZoneDB API</a>.
    818 Commercial network API access is provided
    819 by <a href="https://askgeo.com">AskGeo</a>
    820 and <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
    821 </li>
    822 <li>"<a
    823 href="https://stackoverflow.com/questions/16086962/how-to-get-a-time-zone-from-a-location-using-latitude-and-longitude-coordinates/16086964">How
    824 to get a time zone from a location using latitude and longitude
    825 coordinates?</a>" discusses other geolocation possibilities.</li>
    826 <li><a href="http://statoids.com/statoids.html">Administrative
    827 Divisions of Countries ("Statoids")</a> lists
    828 political subdivision data related to time zones.</li>
    829 <li><a href="https://home.kpn.nl/vanadovv/time/Multizones.html">Time
    830 zone boundaries for multizone countries</a> summarizes legal
    831 boundaries between time zones within countries.</li>
    832 <li><a href="https://manifold.net/info/freestuff.shtml">Manifold Software
    833 &ndash; GIS and Database Tools</a> includes a Manifold-format map of
    834 world time zone boundaries distributed under the
    835 <abbr>GPL</abbr>.</li>
    836 <li>A ship within the <a
    837 href="https://en.wikipedia.org/wiki/Territorial_waters">territorial
    838 waters</a> of any nation uses that nation's time. In international
    839 waters, time zone boundaries are meridians 15&deg; apart, except that
    840 <abbr>UT</abbr>&minus;12 and <abbr>UT</abbr>+12 are each 7.5&deg;
    841 wide and are separated by
    842 the 180&deg; meridian (not by the International Date Line, which is
    843 for land and territorial waters only). A captain can change ship's
    844 clocks any time after entering a new time zone; midnight changes are
    845 common.</li>
    846 </ul>
    847 </section>
    848 
    849 <section>
    850 <h2 id="civil">Civil time concepts and history</h2>
    851 <ul>
    852 <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
    853 Walk through Time</a>
    854 surveys the evolution of timekeeping.</li>
    855 <li>The history of daylight saving time is surveyed in <a
    856 href="http://www.webexhibits.org/daylightsaving/">About Daylight
    857 Saving Time &ndash; History, rationale, laws &amp; dates</a> and summarized in
    858 <a href="http://seizethedaylight.com/dst/">A Brief
    859 History of Daylight Saving Time</a>.</li>
    860 <li><a href="https://www.laphamsquarterly.org/roundtable/time-lords">Time
    861 Lords</a> discusses how authoritarians manipulate civil time.</li>
    862 <li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a>
    863 contains guidelines and best practices for software applications that
    864 deal with civil time.</li>
    865 <li><a href="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
    866 the International Date Line</a> tells the story of the most important
    867 time zone boundary.</li>
    868 <li><a href="http://statoids.com/tconcept.html">Basic Time
    869 Zone Concepts</a> discusses terminological issues behind time zones.</li>
    870 </ul>
    871 </section>
    872 
    873 <section>
    874 <h2 id="national">National histories of legal time</h2>
    875 <dl>
    876 <dt>Australia</dt>
    877 <dd>The Parliamentary Library commissioned a <a
    878 href="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
    879 paper on daylight saving time in Australia</a>.
    880 The Bureau of Meteorology publishes a list of <a
    881 href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
    882 Dates of Daylight Savings Time within Australia</a>.</dd>
    883 <dt>Belgium</dt>
    884 <dd>The Royal Observatory of Belgium maintains a table of time in
    885 Belgium (in
    886 <a href="https://www.astro.oma.be/GENERAL/INFO/nli001a.html"
    887 hreflang="nl">Dutch</a> and <a
    888 href="https://www.astro.oma.be/GENERAL/INFO/fri001a.html"
    889 hreflang="fr">French</a>).</dd>
    890 <dt>Brazil</dt>
    891 <dd>The Time Service Department of the National Observatory
    892 records <a href="http://pcdsh01.on.br/DecHV.html"
    893 hreflang="pt-BR">Brazil's daylight saving time decrees (in
    894 Portuguese)</a>.</dd>
    895 <dt>Canada</dt>
    896 <dd>National Research Council Canada publishes current
    897 and some older information about <a
    898 href="https://nrc.canada.ca/en/certifications-evaluations-standards/canadas-official-time/time-zones-daylight-saving-time">time
    899 zones and daylight saving time</a>.</dd>
    900 <dt>Chile</dt>
    901 <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
    902 <a href="https://www.horaoficial.cl/historia_hora.php" hreflang="es">history of
    903 Chile's official time (in Spanish)</a>.</dd>
    904 <dt>China</dt>
    905 <dd>The Hong Kong Observatory maintains a
    906 <a href="https://www.hko.gov.hk/en/gts/time/Summertime.htm">history of
    907  summer time in Hong Kong</a>,
    908 and Macau's Meteorological and Geophysical Bureau maintains a <a
    909 href="https://www.smg.gov.mo/en/subpage/224/page/174">similar
    910 history for Macau</a>.
    911 Unfortunately the latter is incomplete and has errors.</dd>
    912 <dt>Czech Republic</dt>
    913 <dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
    914 hreflang="cs">When daylight saving time starts and ends (in Czech)</a>
    915 summarizes and cites historical <abbr>DST</abbr> regulations.</dd>
    916 <dt>Germany</dt>
    917 <dd>The National Institute for Science and Technology maintains the <a
    918 href="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
    919 of Legal Time in Germany</a>.</dd>
    920 <dt>Israel</dt>
    921 <dd>The Interior Ministry periodically issues <a
    922 href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
    923 hreflang="he">announcements (in Hebrew)</a>.</dd>
    924 <dt>Malaysia</dt>
    925 <dd>See Singapore <a href="#Singapore">below</a>.</dd>
    926 <dt>Mexico</dt>
    927 <dd>The Investigation and Analysis Service of the Mexican Library of
    928 Congress has published a <a
    929 href="https://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
    930 hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
    931 <dt>Netherlands</dt>
    932 <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
    933 hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
    934 covers the history of local time in the Netherlands from ancient times.</dd>
    935 <dt>New Zealand</dt>
    936 <dd>The Department of Internal Affairs maintains a brief <a
    937 href="https://www.dia.govt.nz/Daylight-Saving-History">History of
    938 Daylight Saving</a>.</dd>
    939 <dt>Palestine</dt>
    940 <dd>The Ministry of Telecom and IT publishes a <a
    941 href="https://mtit.pna.ps/Site/TimeZoon"
    942 hreflang="ar">history of clock changes (in Arabic)</a>.</dd>
    943 <dt>Portugal</dt>
    944 <dd>The Lisbon Astronomical Observatory publishes a
    945 <a href="https://oal.ul.pt/hora-legal/" hreflang="pt">history of
    946 legal time (in Portuguese)</a>.</dd>
    947 <dt>Singapore</dt>
    948 <dd><a id="Singapore"
    949 href="https://web.archive.org/web/20190822231045/http://www.math.nus.edu.sg/~mathelmr/teaching/timezone.html">Why
    950 is Singapore in the "Wrong" Time Zone?</a> details the
    951 history of legal time in Singapore and Malaysia.</dd>
    952 <dt>United Kingdom</dt>
    953 <dd><a
    954 href="https://www.polyomino.org.uk/british-time/">History of
    955 legal time in Britain</a> discusses in detail the country
    956 with perhaps the best-documented history of clock adjustments.</dd>
    957 <dt>United States</dt>
    958 <dd>The Department of Transportation's <a
    959 href="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
    960 Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
    961 <dt>Uruguay</dt>
    962 <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
    963 Navy (SOHMA) publishes an annual <a
    964 href="https://sohma.armada.mil.uy/index.php/servicios/datos-astronomicos" hreflang="es">almanac
    965 (in Spanish)</a>.</dd>
    966 </dl>
    967 </section>
    968 
    969 <section>
    970 <h2 id="costs">Costs and benefits of time shifts</h2>
    971 <p>Various sources argue for and against daylight saving time and time
    972 zone shifts, and many scientific studies have been conducted. This
    973 section summarizes reviews and position statements based on
    974 scientific literature in the area.</p>
    975 <ul>
    976 <li>In 2022 the American Medical Association issued a
    977 <a href="https://www.ama-assn.org/press-center/press-releases/ama-calls-permanent-standard-time">statement
    978 supporting permanent standard time</a> on health grounds.</li>
    979 <li>Carey RN, Sarma KM.
    980 <a href="https://bmjopen.bmj.com/content/7/6/e014319.long">Impact of
    981 daylight saving time on road traffic collision risk: a systematic
    982 review</a>.
    983 <em>BMJ Open.</em> 2017;7(6):e014319. doi:<a href="https://doi.org/10.1136/bmjopen-2016-014319">10.1136/bmjopen-2016-014319</a>.
    984 This reviews research literature and concludes that the evidence
    985 neither supports nor refutes road safety benefits from
    986 shifts in time zones.</li>
    987 <li>Havranek T, Herman D, Irsova D.
    988 <a href="https://www.iaee.org/en/publications/ejarticle.aspx?id=3051">Does
    989 daylight saving save electricity? A meta-analysis.</a>
    990 <em>Energy J.</em> 2018;39(2):35&ndash;61.
    991 doi:<a href="https://doi.org/10.5547/01956574.39.2.thav">10.5547/01956574.39.2.thav</a>.
    992 This analyzes research literature and concludes, "Electricity savings
    993 are larger for countries farther away from the equator, while
    994 subtropical regions consume more electricity because of <abbr>DST</abbr>."</li>
    995 <li>Malow BA. It is time to abolish the clock change and adopt permanent
    996 standard time in the United States: a Sleep Research Society position statement.
    997 <em>Sleep.</em> 2022;45(12):zsac236.
    998 doi:<a href="https://doi.org/10.1093/sleep/zsac236">10.1093/sleep/zsac236</a>.
    999 After reviewing the scientific literature, the Sleep Research Society
   1000 advocates permanent standard time due to its health benefits.
   1001 <li>Rishi MA, Cheng JY, Strang AR <em>et al</em>.
   1002 <a href="https://jcsm.aasm.org/doi/10.5664/jcsm.10898">Permanent standard time
   1003 is the optimal choice for health and safety:
   1004 an American Academy of Sleep Medicine position statement</a>.
   1005 <em>J Clin Sleep Med.</em> 2023-10-31.
   1006 doi:<a href="https://doi.org/10.5664/jcsm.10898">10.5664/jcsm.10898</a>.
   1007 The AASM argues for permanent standard time due to health and safety risks
   1008 and economic costs of both <abbr>DST</abbr> transitions and
   1009 permanent <abbr>DST</abbr>.</li>
   1010 <li>Roenneberg T, Wirz-Justice A, Skene DJ <em>et al</em>.
   1011 <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7205184/">Why
   1012 should we abolish Daylight Saving Time?</a>
   1013 <em>J Biol Rhythms.</em> 2019;34(3):227&ndash;230.
   1014 doi:<a href="https://doi.org/10.1177/0748730419854197">10.1177/0748730419854197</a>.
   1015 The Society for Research on Biological Rhythms
   1016 opposes DST changes and permanent DST, and advocates that governments adopt
   1017 "permanent Standard Time for the health and safety of their citizens".</li>
   1018 </ul>
   1019 </section>
   1020 
   1021 <section>
   1022 <h2 id="precision">Precision timekeeping</h2>
   1023 <ul>
   1024 <li><a
   1025 href="http://leapsecond.com/hpan/an1289.pdf">The
   1026 Science of Timekeeping</a> is a thorough introduction
   1027 to the theory and practice of precision timekeeping.</li>
   1028 <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
   1029 Time 2016</a> contains several freely readable papers.</li>
   1030 <li><a href="https://www.ntp.org"><abbr
   1031 title="Network Time Protocol">NTP</abbr>: The Network
   1032 Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
   1033 discusses how to synchronize clocks of
   1034 Internet hosts.</li>
   1035 <li>The <a href="https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf"><span style="font-variant: small-caps">Huygens</span></a>
   1036 family of software algorithms can achieve accuracy to a few tens of
   1037 nanoseconds in scalable server farms without special hardware.</li>
   1038 <li>The <a
   1039 href="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
   1040 Time Protocol</a> (<abbr
   1041 title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
   1042 can achieve submicrosecond clock accuracy on a local area network
   1043 with special-purpose hardware.</li>
   1044 <li><a
   1045 href="https://datatracker.ietf.org/doc/html/rfc4833">Timezone
   1046 Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
   1047 (Internet <abbr>RFC</abbr> 4833)
   1048 specifies a <a
   1049 href="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
   1050 option for a server to configure
   1051 a client's time zone and daylight saving settings automatically.</li>
   1052 <li><a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
   1053 Scales</a> describes astronomical time scales like
   1054 <abbr title="Terrestrial Dynamic Time">TDT</abbr>,
   1055 <abbr title="Geocentric Coordinate Time">TCG</abbr>, and
   1056 <abbr title="Barycentric Dynamic Time">TDB</abbr>.
   1057 <li>The <a href="https://www.iau.org"><abbr
   1058 title="International Astronomical Union">IAU</abbr></a>'s <a
   1059 href="https://www.iausofa.org"><abbr
   1060 title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
   1061 collection contains C and <a
   1062 href="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
   1063 code for converting among time scales like
   1064 <abbr title="International Atomic Time">TAI</abbr>,
   1065 <abbr>TDB</abbr>, <abbr>TDT</abbr> and
   1066 <abbr>UTC</abbr>. It is freely available under the
   1067 <a href="https://www.iausofa.org/tandc.html">SOFA license</a>.</li>
   1068 <li><a
   1069 href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
   1070 &ndash; Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
   1071 diverse local time
   1072 scales used by each landed mission on Mars.</li>
   1073 <li><a href="http://leapsecond.com">LeapSecond.com</a> is
   1074 dedicated not only to leap seconds but to precise time and frequency
   1075 in general. It covers the state of the art in amateur timekeeping, and
   1076 how the art has progressed over the past few decades.</li>
   1077 <li>The rules for leap seconds are specified in Annex 1 (Time scales) of <a
   1078 href="https://www.itu.int/rec/R-REC-TF.460-6-200202-I/">Standard-frequency
   1079 and time-signal emissions</a>, International Telecommunication Union &ndash;
   1080 Radiocommunication Sector (ITU-R) Recommendation TF.460-6 (02/2002).</li>
   1081 <li><a
   1082 href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
   1083 title="International Earth Rotation and Reference Systems Service">IERS</abbr>
   1084 Bulletins</a> contains official publications of the International
   1085 Earth Rotation and Reference Systems Service, which decides when leap
   1086 seconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds
   1087 via an optional "<code>right</code>" configuration where a computer's internal
   1088 <code>time_t</code> integer clock counts every <abbr>TAI</abbr> second,
   1089 as opposed to the default "<code>posix</code>" configuration
   1090 where the internal clock ignores leap seconds.
   1091 The two configurations agree for timestamps starting with 1972-01-01 00:00:00
   1092 <abbr>UTC</abbr> (<code>time_t</code> 63&thinsp;072&thinsp;000) and diverge for
   1093 timestamps starting with <code>time_t</code> 78&thinsp;796&thinsp;800,
   1094 which corresponds to the first leap second
   1095 1972-06-30 23:59:60 <abbr>UTC</abbr> in the "<code>right</code>" configuration,
   1096 and to
   1097 1972-07-01 00:00:00 <abbr>UTC</abbr> in the "<code>posix</code>" configuration.
   1098 In practice the two configurations also agree for timestamps before
   1099 1972 even though the historical situation is messy, partly because
   1100 neither <abbr>UTC</abbr> nor <abbr>TAI</abbr>
   1101 is well-defined for sufficiently old timestamps.</li>
   1102 <li><a href="https://developers.google.com/time/smear">Leap Smear</a>
   1103 discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
   1104 leap second so that they disagree with <abbr>UTC</abbr> by at most a
   1105 half second, even though every <abbr>POSIX</abbr> minute has exactly
   1106 sixty seconds. This approach works with the default <code><abbr>tz</abbr></code>
   1107 "<code>posix</code>" configuration, is <a
   1108 href="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
   1109 the <abbr>NTP</abbr> reference implementation, <a
   1110 href="https://github.com/google/unsmear">supports</a> conversion between
   1111 <abbr>UTC</abbr> and smeared <abbr>POSIX</abbr> timestamps, and is used by major
   1112 cloud service providers. However, according to
   1113 <a href="https://datatracker.ietf.org/doc/html/rfc8633#section-3.7.1">&sect;3.7.1 of
   1114 Network Time Protocol Best Current Practices</a>
   1115 (Internet <abbr>RFC</abbr> 8633), leap smearing is not suitable for
   1116 applications requiring accurate <abbr>UTC</abbr> or civil time,
   1117 and is intended for use only in single, well-controlled environments.</li>
   1118 <li>The <a
   1119 href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
   1120 Second Discussion List</a> covers <a
   1121 href="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
   1122 and Klepczynski's 1999 proposal to discontinue leap seconds</a>,
   1123 discussed further in
   1124 <a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
   1125 leap second: its history and possible future</a>.
   1126 <a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
   1127 might be redefined
   1128 without Leap Seconds</a> gives pointers on this
   1129 contentious issue.
   1130 The General Conference on Weights and Measures
   1131 <a href="https://www.bipm.org/en/cgpm-2022/resolution-4">voted in 2022</a>
   1132 to discontinue the use of leap seconds by 2035, replacing them with an
   1133 as-yet-undetermined scheme some time after the year 2135.
   1134 </li>
   1135 </ul>
   1136 </section>
   1137 
   1138 <section>
   1139 <h2 id="notation">Time notation</h2>
   1140 <ul>
   1141 <li>The <a id="CLDR" href="https://cldr.unicode.org">Unicode Common Locale Data
   1142 Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
   1143 zone names, abbreviations, identifiers, and formats. For example, it
   1144 contains French translations for "Eastern European Summer Time",
   1145 "<abbr title="Eastern European Summer Time">EEST</abbr>", and
   1146 "Bucharest". Its
   1147 <a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
   1148 charts</a> show these values for many locales. Data values are available in
   1149 both <abbr title="Locale Data Markup Language">LDML</abbr>
   1150 (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
   1151 <li>
   1152 <a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
   1153 the international standard date and time notation</a> covers
   1154 <a
   1155 href="https://www.iso.org/standard/70907.html"><em><abbr
   1156 title="International Organization for Standardization">ISO</abbr>
   1157 8601-1:2019 &ndash; Date and time &ndash; Representations for information
   1158 interchange &ndash; Part 1: Basic rules</em></a>.</li>
   1159 <li>
   1160 <a href="https://www.w3.org/TR/xmlschema/#dateTime"><abbr>XML</abbr>
   1161 Schema: Datatypes &ndash; dateTime</a> specifies a format inspired by
   1162 <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
   1163 <li><a href="https://datatracker.ietf.org/doc/html/rfc5322#section-3.3">&sect;3.3 of
   1164 Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
   1165 specifies the time notation used in email and <a
   1166 href="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
   1167 headers.</li>
   1168 <li>
   1169 <a href="https://datatracker.ietf.org/doc/html/rfc3339">Date and Time
   1170 on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
   1171 specifies an <abbr>ISO</abbr> 8601
   1172 profile for use in new Internet
   1173 protocols.</li>
   1174 <li>
   1175 <a href="https://web.archive.org/web/20190130042457/https://www.hackcraft.net/web/datetime/">Date &amp; Time
   1176 Formats on the Web</a> surveys web- and Internet-oriented date and time
   1177 formats.</li>
   1178 <li>Alphabetic time zone abbreviations should not be used as unique
   1179 identifiers for <abbr>UT</abbr> offsets as they are ambiguous in
   1180 practice. For example, in English-speaking North America
   1181 "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
   1182 but in China it denotes 8 hours ahead of <abbr>UT</abbr>,
   1183 and French-speaking North Americans prefer
   1184 "<abbr title="Heure Normale du Centre">HNC</abbr>" to
   1185 "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
   1186 database contains English abbreviations for many timestamps;
   1187 unfortunately some of these abbreviations were merely the database maintainers'
   1188 inventions, and these have been removed when possible.</li>
   1189 <li>Numeric time zone abbreviations typically count hours east of
   1190 <abbr>UT</abbr>, e.g., +09 for Japan and
   1191 &minus;10 for Hawaii. However, the <abbr>POSIX</abbr>
   1192 <code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
   1193 For example, one might use <code><abbr>TZ</abbr>="<abbr
   1194 title="Japan Standard Time">JST</abbr>-9"</code> and
   1195 <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
   1196 for Japan and Hawaii, respectively. If the
   1197 <code><abbr>tz</abbr></code> database is available, it is usually better to use
   1198 settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
   1199 <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
   1200 confusion, handle old timestamps better, and insulate you better from
   1201 any future changes to the rules. One should never set
   1202 <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
   1203 <code>"GMT-9"</code>, though, since this would incorrectly imply that
   1204 local time is nine hours ahead of <abbr>UT</abbr> and the time zone
   1205 is called "<abbr>GMT</abbr>".</li>
   1206 </ul>
   1207 </section>
   1208 
   1209 <section>
   1210 <h2 id="see-also">See also</h2>
   1211 <ul>
   1212 <li><a href="theory.html">Theory and pragmatics of the
   1213 <code><abbr>tz</abbr></code> code and data</a></li>
   1214 <li><a href="tz-art.html">Time and the Arts</a></li>
   1215 </ul>
   1216 </section>
   1217 
   1218 <footer>
   1219 <hr>
   1220 This web page is in the public domain, so clarified as of
   1221 2009-05-17 by Arthur David Olson.
   1222 <br>
   1223 Please send corrections to this web page to the
   1224 <a href="mailto:tz (a] iana.org">time zone mailing list</a>.
   1225 </footer>
   1226 </body>
   1227 </html>
   1228