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<p>You may also find the following article to be useful:</p>
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<p><a href="http://www.iana.org/time-zones/repository/tz-how-to.html" class="OWAAutoLink" id="LPlnk892092" previewremoved="true">http://www.iana.org/time-zones/repository/tz-how-to.html</a><br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> tz-bounces@iana.org <tz-bounces@iana.org> on behalf of Guy Harris <guy@alum.mit.edu><br>
<b>Sent:</b> Tuesday, November 1, 2016 2:20 PM<br>
<b>To:</b> Gintare Statkute<br>
<b>Cc:</b> tz@iana.org<br>
<b>Subject:</b> Re: [tz] www.timeanddate.com provides different data</font>
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<div class="PlainText">On Nov 1, 2016, at 5:26 AM, Gintare Statkute <g.statkute@gmail.com> wrote:<br>
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> On this website i find the following data:<br>
> <a href="https://www.timeanddate.com/time/zone/uk/london" id="LPlnk245536" previewremoved="true">
https://www.timeanddate.com/time/zone/uk/london</a>
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<a id="LPUrlAnchor_14781042902030.3708792244768906" href="https://www.timeanddate.com/time/zone/uk/london" target="_blank" style="text-decoration: none;">Daylight saving time dates for United Kingdom – England ...</a></div>
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www.timeanddate.com</div>
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Historic, present and future dates for daylight saving time and clock changes. Time changes between years 2015 and 2019 in United Kingdom – England – London are ...</div>
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> <br>
> 2015Sun, 29 Mar, 01:00GMT → BST+1 hour (DST start)UTC+1h <br>
> Sun, 25 Oct, 02:00BST → GMT-1 hour (DST end)UTC<br>
> 2016 Sun, 27 Mar, 01:00GMT → BST+1 hour (DST start)UTC+1h <br>
> Sun, 30 Oct, 02:00BST → GMT-1 hour (DST end)UTC<br>
> 2017 Sun, 26 Mar, 01:00GMT → BST+1 hour (DST start)UTC+1h <br>
> Sun, 29 Oct, 02:00BST → GMT-1 hour (DST end)UTC<br>
> 2018 Sun, 25 Mar, 01:00GMT → BST+1 hour (DST start)UTC+1h <br>
> Sun, 28 Oct, 02:00BST → GMT-1 hour (DST end)UTC<br>
> 2019 Sun, 31 Mar, 01:00GMT → BST+1 hour (DST start)UTC+1h <br>
> Sun, 27 Oct, 02:00BST → GMT-1 hour (DST end)UTC<br>
> <br>
> As you can see, the Europe/London time change rule is different every year .<br>
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2015: the UK changes from standard time to summer time on the last Sunday in March.<br>
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2016: the UK changes from standard time to summer time on the last Sunday in March.<br>
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2017: the UK changes from standard time to summer time on the last Sunday in March.<br>
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2018: the UK changes from standard time to summer time on the last Sunday in March.<br>
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2019: the UK changes from standard time to summer time on the last Sunday in March.<br>
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That's not different every year. The date of the last Sunday in March is different every year, but that's just the way the Gregorian calendar works.<br>
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> But i can not find this information on yor data distribution.<br>
> <a href="https://www.iana.org/time-zones" id="LPlnk15151" previewremoved="true">
https://www.iana.org/time-zones</a>
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<a id="LPUrlAnchor_14781042905300.34058342936268127" href="https://www.iana.org/time-zones" target="_blank" style="text-decoration: none;">IANA — Time Zone Database</a></div>
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www.iana.org</div>
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Time Zone Database. The Time Zone Database (often called tz or zoneinfo) contains code and data that represent the history of local time for many representative ...</div>
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> <br>
> For europe, london you give:<br>
> # Zone NAME GMTOFF RULES FORMAT [UNTIL]<br>
> Zone Europe/London -0:01:15 - LMT 1847 Dec 1 0:00s<br>
> 0:00 GB-Eire %s 1968 Oct 27<br>
> 1:00 - BST 1971 Oct 31 2:00u<br>
> 0:00 GB-Eire %s 1996<br>
> 0:00 EU GMT/BST<br>
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That says that, from 1996 on, they used the "EU" rules. Those should also be in the "europe" file; the 2016g file says:<br>
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# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S<br>
Rule EU 1977 1980 - Apr Sun>=1 1:00u 1:00 S<br>
Rule EU 1977 only - Sep lastSun 1:00u 0 -<br>
Rule EU 1978 only - Oct 1 1:00u 0 -<br>
Rule EU 1979 1995 - Sep lastSun 1:00u 0 -<br>
Rule EU 1981 max - Mar lastSun 1:00u 1:00 S<br>
Rule EU 1996 max - Oct lastSun 1:00u 0 -<br>
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So, from 1981 on, the "EU" rules specify that the time changes to summer time at 1:00 UTC on the last Sunday in March.<br>
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As Paul Eggert indicated, the "zic" man page describes how those files work.<br>
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