365 lines
17 KiB
HTML
365 lines
17 KiB
HTML
<?xml version="1.0" encoding="US-ASCII"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<title>Sources for Time Zone and Daylight Saving Time Data</title>
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<link rel="schema.DC" href="http://purl.org/DC/elements/1.1/" />
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<meta http-equiv="Content-type" content='text/html; charset="US-ASCII"' />
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<meta name="DC.Creator" content="Eggert, Paul" />
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<meta name="DC.Contributor" content="Olson, Arthur David" />
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<meta name="DC.Date" content="2001-05-30" />
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<meta name="DC.Description"
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content="Sources of information about time zones and daylight saving time" />
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<meta name="DC.Identifier" content="http://www.twinsun.com/tz/tz-link.htm" />
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<meta name="Keywords"
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content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo" />
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</head>
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<body>
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<h1>Sources for Time Zone and Daylight Saving Time Data</h1>
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<address>
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@(#)tz-link.htm 7.34
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</address>
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<p>
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Please send corrections to this web page to the
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<a href="mailto:tz@elsie.nci.nih.gov">time zone mailing list</a>.
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</p>
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<h2>The <code>tz</code> database</h2>
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<p>
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The public-domain time zone database contains code and data
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that represent the history of local time
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for many representative locations around the globe.
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It is updated periodically to reflect changes made by political bodies
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to UTC offsets and daylight-saving rules.
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This database (often called <code>tz</code> or <code>zoneinfo</code>)
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is used by several implementations,
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including
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<a href="http://www.linux.org/">GNU/Linux</a>,
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<a href="http://www.freebsd.org/">FreeBSD</a>,
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<a href="http://www.netbsd.org/">NetBSD</a>,
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<a href="http://www.openbsd.org/">OpenBSD</a>,
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<a href="http://www.delorie.com/djgpp/">DJGPP</a>,
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<a href="http://www.hp.com/products1/unix/operating/index.html">HP-UX</a>,
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<a href="http://www.sgi.com/developers/technology/irix.html">IRIX</a>,
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<a href="http://www.caldera.com/products/openunix/">Open UNIX</a>,
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<a href="http://www.sun.com/solaris/">Solaris</a>, and
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<a href="http://www.tru64unix.compaq.com/">Tru64</a>.</p>
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<p>
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Each location in the database represents a national region where all
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clocks keeping local time have agreed since 1970.
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Locations are identified by continent or ocean and then by the name of
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the location, which is typically the largest city within the region.
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For example, <code>America/New_York</code>
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represents most of the US eastern time zone;
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<code>America/Indianapolis</code> represents most of Indiana, which
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uses eastern time without daylight saving time (DST);
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<code>America/Detroit</code> represents most of Michigan, which uses
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eastern time but with different DST rules in 1975;
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and other entries represent smaller regions like Starke County,
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Kentucky, which switched from central to eastern time in 1991.
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To use the database, set the <code>TZ</code> environment variable to
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the location's full name, e.g., <code>TZ="America/New_York"</code>.</p>
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<p>
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In the <code>tz</code> database's
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<a href="ftp://elsie.nci.nih.gov/pub/">FTP distribution</a>,
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the code is in the file <code>tzcode<var>C</var>.tar.gz</code>,
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where <code><var>C</var></code> is the code's version;
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similarly, the data are in <code>tzdata<var>D</var>.tar.gz</code>,
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where <code><var>D</var></code> is the data's version.
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The following shell commands download
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these files to a GNU/Linux or similar host; see the downloaded
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<code>README</code> file for what to do next.</p>
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<pre style="margin-left: 2em"><code><a href="http://www.gnu.org/software/wget/">wget</a> 'ftp://elsie.nci.nih.gov/pub/tz*.tar.gz'
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<a href="http://www.gnu.org/software/gzip/">gzip</a> -dc tzcode*.tar.gz | <a href="http://www.gnu.org/software/tar/">tar</a> -xf -
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gzip -dc tzdata*.tar.gz | tar -xf -
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</code></pre>
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<p>
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The code lets you compile the <code>tz</code> source files into
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machine-readable binary files, one for each location. It also lets
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you read a <code>tz</code> binary file and interpret time stamps for that
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location.</p>
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<p>
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The data are by no means authoritative. If you find errors, please
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send changes to the <a href="mailto:tz@elsie.nci.nih.gov">time zone
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mailing list</a>. You can also <a
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href="mailto:tz-request@elsie.nci.nih.gov">subscribe</a> to the
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mailing list, or retrieve the <a
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href="ftp://elsie.nci.nih.gov/pub/tzarchive.gz">archive of old
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messages</a> (in gzip compressed format).</p>
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<p>
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The Web has several other sources for time zone and daylight saving time data.
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Here are some recent links that may be of interest.
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</p>
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<h2>Web pages using recent versions of the <code>tz</code> database</h2>
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<ul>
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<li><a href="http://www.bsdi.com/date/">Date and Time Gateway</a> is a
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text-based point-and-click interface to tables of current time
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throughout the world.</li>
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<li><a href="http://sandbox.xerox.com/stewart/tzconvert.cgi">Timezone
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Converter</a> is a similar interface, with source code
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written in <a href="http://www.perl.org/">Perl</a>, using what Paul
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Stewart calls the "20-line hack no one will let me forget".</li>
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<li>Fancier web interfaces, roughly in ascending order of complexity, include:
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<ul>
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<li><a href="http://www.hilink.com.au/times/">Local Times Around the
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World</a></li>
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<li><a href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current Time in 1000 Places</a></li>
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<li><a href="http://timezoneconverter.com/">Time Zone Converter</a></li>
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</ul></li>
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<li><a href="http://www.tick2tock.com/cgi-bin/TZConverter">Tick2Tock
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time zone converter</a> is a multilingual interface.</li>
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<li><a href="http://www.holidayfestival.com/">The Worldwide Holiday
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& Festival Site</a> lists DST-related clock changes along with
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holidays.</li>
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<li><a href="http://www.timeanddate.com/worldclock/">The World Clock</a>
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is a web interface to a time zone database derived from
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<code>tz</code>'s.</li>
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</ul>
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<h2>Other <code>tz</code> compilers</h2>
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<ul>
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<li><a href="http://primates.ximian.com/~damon/icalendar/">Olson ->
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VTIMEZONE Converter</a> describes a program Vzic that
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compiles <code>tz</code> source into VTIMEZONE text as specified by
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the <a href="ftp://ftp.isi.edu/in-notes/rfc2445.txt">iCalendar</a>
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specification published by the <a
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href="http://www.ietf.org/html.charters/calsch-charter.html">IETF
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Calendaring and Scheduling Working Group</a>. Vzic is freely
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available under the <a href="http://www.gnu.org/copyleft/gpl.html">GNU
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General Public License (GPL)</a>.</li>
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<li>Possible XML schemata for the <code>tz</code> data include <a
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href="http://www.w3.org/2000/01/foo">one</a> sketched out by <a
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href="http://www.w3.org/People/Berners-Lee/">Tim Berners-Lee</a> and
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<a
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href="http://developer.iplanet.com/docs/wpapers/calendar/ietf.txt">another</a>
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used by the <a
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href="http://www.iplanet.com/products/iplanet_calendar/">iPlanet
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Calendar Server</a>.</li>
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</ul>
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<h2>Other <code>tz</code> binary file readers</h2>
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<ul>
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<li>The <a href="http://www.gnu.org/software/libc/">GNU C Library</a>
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has an independent, thread-safe implementation of
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a <code>tz</code> binary file reader.
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This library is freely available under the
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<a href="http://www.gnu.org/copyleft/lesser.html">
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GNU Lesser General Public License (LGPL)</a>,
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and is widely used in GNU/Linux systems.</li>
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<li><a href="http://www.bmsi.com/java/#TZ">ZoneInfo.java</a>
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is a <code>tz</code> binary file reader written in Java.
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It is freely available under the GNU LGPL.</li>
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</ul>
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<h2>Other <code>tz</code>-based time zone conversion software</h2>
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<ul>
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<li><a
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href="http://www1.tip.nl/~t876506/AboutTimeZonesHC.html">HyperCard
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time zones calculator</a> is a HyperCard stack.</li>
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<li><a
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href="http://www20.Brinkster.com/timezone50/">Time Zone Converter</a> is a
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Microsoft Windows program.</li>
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</ul>
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<h2>Other time zone databases</h2>
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<ul>
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<li><a href="http://www.astro.ch/cgi-bin/atlw3/aq.cgi?lang=e">Astrodienst
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- Atlas Query</a> is Astrodienst's Web version of Shanks's
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excellent time zone history atlases published in both <a
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href="http://astrocom.com/software/pcatlas.html">computer</a> and <a
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href="http://astrocom.com/books/xrefa.htm#SHANKS">book</a> form by <a
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href="http://astrocom.com/">Astro Communications Services</a>.</li>
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<li><a href="http://worldtime.com/">WORLDTIME: interactive atlas,
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time info, public holidays</a>
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contains information on local time, sunrise and sunset,
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and public holidays in several hundred cities around the world.</li>
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<li><a href="http://www.worldtimeserver.com/">World Time Server</a>
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is another time zone database.</li>
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<li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a>
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contains data from the Time Service Department of the US Naval Observatory
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(USNO), used as the source
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for the <code>usno*</code> files in the <code>tz</code> distribution.</li>
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<li><a href="http://www.airportcitycodes.com/aaa/">Airlines, Airplanes
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and Airports</a> lists current standard times for thousands of
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airports around the world. This seems to be derived from
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the <a href="http://www.iata.org/sked/ssim.htm">Standard
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Schedules Information Manual</a> of the
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the <a href="http://www.iata.org/">International Air Transport
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Association</a>,
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which gives current time zone rules for
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all the airports served by commercial aviation.</li>
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</ul>
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<h2>Maps</h2>
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<ul>
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<li>The <a href="http://www.odci.gov/">United States Central
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Intelligence Agency (CIA)</a> publishes a <a
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href="http://www.odci.gov/cia/publications/factbook/ref/pdf/802801.pdf">time
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zone map</a>; the
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<a
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href="http://www.lib.utexas.edu/maps/world.html">Perry-Castañeda
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Library Map Collection</a>
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of the University of Texas at Austin has copies of
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recent editions.
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The pictorial quality is good,
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but the maps do not indicate summer time,
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and parts of the data are a few years out of date.</li>
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<li><a href="http://wwg.lgg.ru/russia/timezone.html"
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hreflang="ru">Map of Russian Federation time zones (in Russian)</a>
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has a wealth of information about Russian time zones.</li>
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</ul>
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<h2>Time zone boundaries</h2>
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<ul>
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<li>Manifold.net's <a
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href="http://www.manifold.net/download/freemaps.html">Free Maps and
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GIS Data</a> includes a Manifold-format map of world time zone
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boundaries distributed under the GPL. The GeoCommunity's <a
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href="http://software.geocomm.com/data/intl_timezones.html">International
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Time Zones</a> publishes the same data in other formats.</li>
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<li>The US Geological Survey's National Atlas of the United States
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publishes the <a href="http://www.nationalatlas.gov/timeznm.html">Time
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Zones of the United States</a> in the public domain.</li>
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<li>The National Weather Service publishes <a
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href="http://isl715.nws.noaa.gov/mapdata/newcat/county/county_all.htm">outlines
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of US counties and their time zones</a> in the public domain.</li>
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<li>The GeoCommunity lists several commercial sources for <a
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href="http://spatialnews.geocomm.com/features/timezones/">International
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Time Zones and Time Zone Data</a>.</li>
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</ul>
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<h2>Daylight saving time concepts and history</h2>
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<ul>
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<li><a href="http://webexhibits.com/daylightsaving/">About Daylight
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Saving Time - History, rationale, laws and dates</a>
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is a good overall history of DST.</li>
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<li><a href="http://toi.iriti.cnr.it/">The
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Time of Internet</a>
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contains good descriptions of Time Zones and daylight saving time,
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with diagrams.
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The time zone map is out of date, however.</li>
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<li><a href="http://www.phys.uu.nl/~vgent/idl/idl.htm">A History of
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the International Date Line</a> tells the story of the most important
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time zone boundary.</li>
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<li>A few countries have well-documented histories of legal time.
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<dl>
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<dt>Australia</dt>
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<dd><a
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href="http://www.dstc.qut.edu.au/DST/marg/daylight.html#more">Australia's
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Daylight Saving Times</a> contains pointers to government records and to
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histories of daylight saving.</dd>
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<dt>Belgium</dt>
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<dd>The Royal Observatory of Belgium maintains a table of <a
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href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html"
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hreflang="nl">time in Belgium (in Dutch)</a>.</dd>
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<dt>Brazil</dt>
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<dd>The Time Service Department of the National Observatory
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records <a href="http://pcdsh01.on.br/DecHV.html"
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hreflang="pt-BR">Brazil's daylight saving time decrees (in
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Portuguese)</a>.</dd>
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<dt>Canada</dt>
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<dd>The Institute for National Measurement Standards publishes current
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and some older information about <a
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href="http://www.nrc.ca/inms/time/tze.html">Time Zones and Daylight
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Saving Time</a>.</dd>
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<dt>Germany</dt>
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<dd>The National Institute for Science and Technology maintains the <a
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href="http://www.ptb.de/en/org/4/43/432/lega.htm">Realisation of
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Legal Time in Germany</a>.</dd>
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<dt>Israel</dt>
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<dd>The Ministry of Interior periodically issues <a
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href="ftp://ftp.huji.ac.il/pub/tz/announcements"
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hreflang="he">announcements (in Hebrew)</a>.</dd>
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<dt>Mexico</dt>
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<dd>The Investigation and Analysis Service of the Mexican Library of
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Congress has published a <a
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href="http://www.cddhcu.gob.mx/bibliot/publica/inveyana/polisoc/horver/"
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hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
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<dt>Netherlands</dt>
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<dd><a href="http://www.phys.uu.nl/~vgent/wettijd/wettijd.htm"
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hreflang="nl">Legal time in the Netherlands (in Dutch)</a>
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covers the history of local time in the Netherlands from ancient times.</dd>
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<dt>United Kingdom</dt>
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<dd><a
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href="http://student.cusu.cam.ac.uk/~jsm28/british-time/">History of
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legal time in Britain</a> is an excellent discussion for the country
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with perhaps the best-documented history of clock adjustments.
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The National Physical Laboratory also maintains an <a
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href="http://www.npl.co.uk/npl/ctm/summer_time_archive.html">archive
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of summer time dates</a>.</dd>
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</dl></li>
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</ul>
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<h2>Precision timekeeping</h2>
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<ul>
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<li><a
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href="http://literature.agilent.com/litwebbin/purl.cgi?org_id=tmo&pub_id=5965-7984E">The
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Science of Timekeeping</a> is an excellent and thorough introduction
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to the theory and practice of precision timekeeping.</li>
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<li><a href="http://www.ntp.org/">Time Server</a> discusses
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the Network Time Protocol (NTP), used to synchronize clocks of
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Internet hosts.</li>
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<li><a href="http://ecco.bsee.swin.edu.au/chronos/GMT-explained.html">A
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Few Facts Concerning GMT, UT, and the RGO</a>
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answers questions like "What is the difference between GMT and UTC?"</li>
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<li><a
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href="http://sadira.gb.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
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Times</a> explains more abstruse astronomical time scales like TT, TCG,
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and TDB.</li>
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<li>The <a href="http://www.iau.org/">IAU</a>'s <a
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href="http://www.iau-sofa.rl.ac.uk/">Standards Of Fundamental
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Astronomy</a> (SOFA) initiative publishes Fortran code for converting
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among time scales like TAI, TDB, TT and UTC.</li>
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<li><a href="http://www.jpl.nasa.gov/basics/bsf2-3.htm">Basics of
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Space Flight - Reference Systems - Time Conventions</a>
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briefly explains interplanetary space flight timekeeping.</li>
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<li><a
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href="http://hpiers.obspm.fr/eop-pc/products/bulletins.html">Bulletins
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maintained by the IERS EOP (PC)</a> contains official publications of
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the Earth Orientation Parameters Product Center of the
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International Earth Rotation Service, the committee that decides
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when leap seconds occur.</li>
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<li>The <a
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href="http://clockdev.usno.navy.mil/archives/leapsecs.html">Leap
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Second Discussion List</a> covers <a
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href="http://clockdev.usno.navy.mil/cgi-bin/wa.exe?A3=ind00&L=leapsecs&P=28537&E=2&B=------_=_NextPart_000_01C0781C.F015C5B0&N=GPS-Nov99_Innov.pdf&T=application/octet-stream">McCarthy
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and Klepczynski's proposal to discontinue leap seconds</a>
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(which requires discussion list membership to read).
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This proposal is being studied by the URSI Commission J <a
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href="http://space.mit.edu/URSI/leapsecond.html">Working Group on the
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Leap Second</a>, and the IAU
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has plans to report on this proposal by 2003.</li>
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</ul>
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<h2>Time notation</h2>
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<ul>
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<li>
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<a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A Summary of
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the International Standard Date and Time Notation</a> is a good
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summary of ISO
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8601:1988 - Data elements and interchange formats - Information interchange
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- Representation of dates and times (which has been superseded by
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<a href="http://www.iso.ch/cate/d26780.html">ISO 8601:2000</a>).</li>
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<li>
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Section 3.3 of <a
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href="ftp://ftp.isi.edu/in-notes/rfc2822.txt">Internet RFC 2822</a>
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specifies the time notation used in email and <a
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href="ftp://ftp.isi.edu/in-notes/rfc2616.txt">HTTP</a> headers.</li>
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<li>
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<a
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href="ftp://ftp.isi.edu/internet-drafts/draft-ietf-impp-datetime-05.txt">Date
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and Time on the Internet: Timestamps</a> proposes an ISO 8601 profile
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for use in new Internet protocols.</li>
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<li>
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Alphabetic time zone abbreviations should not be used as unique
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identifiers for UTC offsets as they are ambiguous in practice. For
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example, "EST" denotes 5 hours behind UTC in English-speaking North
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America, but it denotes 10 or 11 hours ahead of UTC in Australia;
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and French-speaking North Americans prefer "HNE" to "EST". For
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compatibility with <a href="http://www.pasc.org/#POSIX">POSIX</a> the
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<code>tz</code> database contains English abbreviations for all time
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stamps but in many cases these are merely inventions of the database
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maintainers.</li>
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</ul>
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<h2>Related indexes</h2>
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<ul>
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<li><a href="http://dmoz.org/Reference/Time/">Open Directory -
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Reference: Time</a></li>
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<li><a href="tz-art.htm">Time and the Arts</a></li>
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<li><a href="http://dir.yahoo.com/Science/Measurements_and_Units/Time/Time_Zones/">Yahoo! - Science:Measurements and Units:Time:Time Zones</a></li>
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</ul>
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