Text 28117, 112 rader
Skriven 2012-04-20 13:37:57 av Michiel van der Vlist (2:280/5555)
     Kommentar till en text av Roy Witt (1:387/22)
Ärende: TZUTC Kludge
====================
Hello Roy,

On Thursday April 19 2012 03:01, you wrote to me:

 MvdV>> Indeed, the transition times from DST to ST and back are not
 MvdV>> uniform. Here in Europe (Except the UK) the spring transition
 MvdV>> is on the last Sunday in March and the fall transition on the
 MvdV>> last Sunday in October.

However, even that varies. Between 1981 and 1995, DST ended on the last Sunday
in September. To show that it is very hard for programmers to keep up with the
politicians, even Microsoft got it wrong in 1996. Windows rest DST one month
early.

 RW> And here DST begins on the 2nd Sunday in March and ends on the first
 RW> Sunday in November.

But how boiut other countries? Not all countries have DST and the transition
times vary wildly. Try to figure it out for Mexico...

 RW>>> Using my DX World Map posted on the wall over this PC, just
 RW>>> knowing your country is close enough.

 MvdV>> aparently not...

Plus that my DX world ma0 is over 30 years old. A lot has changed since then.

 RW> The time zones on the map don't follow local time zone lines, they
 RW> follow degrees before and after UTC 0. i.e. the center of the -6 hour
 RW> coordinates is 90 degrees west of UTC 0, but -6 hours UTC begins
 RW> closer to New Orleans than San Antonio, which is closer to 90 degrees.

 RW> Which doesn't reflect the true CST which begins on the Eastern border
 RW> with Louisiana and ends somewhere in west Texas, putting El Paso,
 RW> Texas in the Mountain Standard Time zone.

Same for other countries. Time zone bouderies usually follow national borders,
not line of longitude.

 RW> I would  suspect the same is true of local time zones in Europe, to
 RW> accommodate a convenience for heavily populated areas.

Of course. But if you look at the map, you can see that Spain is MET and the UK
is WET, despite the fact that Spain is directly south of the UK. Portugal OTOH
is WET.

 RW>>> The time chart at the bottom of that map shows western Europe
 RW>>> standard time is either 0 or 1 hour before 0.

 MvdV>> Eh.. no. My country is not on Western European Time, it is on
 MvdV>> Middle European time. +0100 in winter and +0200 in summer...

 RW> Right. 0 UTC is in Greenwich, England and 0100 begins somewhere around
 RW> 7.5 degrees east of there. i.e. South Africa is split up the middle by
 RW> the 0100-0200 line at 22.5 degrees, but I'll bet the whole country is
 RW> in one time zone.

It is. +0200

 RW>>> Interesting is how Ireland is split up the middle, either 0 or
 RW>>> -1...how they deal with that I don't know.

 MvdV>> Your chart is wrong. All of Ireland is on the same time. Same
 MvdV>> time as the UK.

 RW> Which is a local time zone difference for convenience of the
 RW> population.

As i said, time zones follow national bounderies rather than lines of
longitude. Only big countries like the US, Russia and Australia have more than
one time zone.

 RW>>> I know that your country is in the 0100 time zone. See above.

 MvdV>> But how do you know?

 RW> The map includes a close-up view of western Europe. Time zones are
 RW> shown by a dotted line, which is self explantory in the "Legends"
 RW> column.

 RW>  ----------- Time Zone Boundry

 MvdV>> Where do you get the information about the DST transition
 MvdV>> times?

 RW> That's a guessing game, but usually close to the same times as the
 RW> transition takes place here, give or take a week or so...

You could be three weeks off in March (2nd Sunday, vs last Sunday).

En before 1996, you would be over a month off in fall. (last Sunday in Sept vs
first in November)

 RW> and just like Arizona (MST) there are probably places around the world
 RW> that don't have DST.

There are LOTS of places that do not have DST.

 MvdV>> Probably. There is also the matter of on-line bank transfers. I
 MvdV>> just made a payment 5 minutes before the deadline. Had I not
 MvdV>> used local time, I would have been late...

 RW> I use paper...which is my choice.

To each his own. I have learned to appricate the almost instantaneous
electronic transfers.


Cheers, Michiel

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