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From: mi...@crash.cts.com (Mike Lemons)
Subject: When Does Daylight Savings Time Change?
Organization: Multicellular, carbon-based lifeform
Date: Fri, 2 Sep 1994 21:16:56 GMT
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I'm writing a routine to do an automatic daylight savings time change. 
Unfortunately, I don't understand the rules very well.  On the last
Saturday in October, you set the clock back one hour.  On the first
Saturday in April, you set the clock forward one hour.  The problem with
that description is that the change actually occurs at 3am or 2am on
the following Sunday.  What happens when Saturday and Sunday are in
different months?

For example, would you set the clock back at 3am on the 25th or Sep 1st?
10/31/98 is the last Saturday in October:
   October 1998
 S  M Tu  W Th  F  S
             1  2  3
 4  5  6  7  8  9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31


Would you set the clock forward at 2am on the 1st or 8th?
4/01/01 is the first Sunday in April:
   April 2001
 S  M Tu  W Th  F  S
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30

------------------------------------------------------------------------------
mi...@crash.cts.com   | Don't confuse making   | "Why should we bother to do
Mike Lemons           | things illegal with    | anything if it's all just
                      | leadership and         | going to fall in a black hole
                      | governing a nation.    | some day?" - an ex girlfriend

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From: w...@netcom.com (William J. Evans)
Subject: Re: When Does Daylight Savings Time Change?
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Mike Lemons (mi...@crash.cts.com) wrote:
: I'm writing a routine to do an automatic daylight savings time change. 
: Unfortunately, I don't understand the rules very well.  On the last
: Saturday in October, you set the clock back one hour.  On the first
: Saturday in April, you set the clock forward one hour.  The problem with
: that description is that the change actually occurs at 3am or 2am on
: the following Sunday.  What happens when Saturday and Sunday are in
: different months?

Forget the Saturday stuff.

On the first Sunday in April, in the wee hours of the morning, when
it's 2:00am, set the clock to 3:00am.  On the last Sunday in October,
when it's 2:00am, set the clock to 1:00am (not 3:00 to 2:00).

In the United States, only Arizona and Indiana do not use Daylight
Savings Time.

-- Bill Evans

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From: dan...@cernapo.cern.ch (Dan Pop)
Subject: Re: When Does Daylight Savings Time Change?
Message-ID: <CvMAsJ.94r@news.cern.ch>
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Date: Sun, 4 Sep 1994 18:17:07 GMT
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In <wjeCvM172....@netcom.com> w...@netcom.com (William J. Evans) writes:

>Mike Lemons (mi...@crash.cts.com) wrote:
>: I'm writing a routine to do an automatic daylight savings time change. 
>: Unfortunately, I don't understand the rules very well.  On the last
>: Saturday in October, you set the clock back one hour.  On the first
>: Saturday in April, you set the clock forward one hour.  The problem with
>: that description is that the change actually occurs at 3am or 2am on
>: the following Sunday.  What happens when Saturday and Sunday are in
>: different months?
>
>Forget the Saturday stuff.
>
>On the first Sunday in April, in the wee hours of the morning, when
>it's 2:00am, set the clock to 3:00am.  On the last Sunday in October,
>when it's 2:00am, set the clock to 1:00am (not 3:00 to 2:00).
>
>In the United States, only Arizona and Indiana do not use Daylight
>Savings Time.

And in Europe it's the last Sunday in March and the last Sunday in
September, at midnight (0:00am --> 1:00am and 1:00am --> 0:00am).

Dan
--
Dan Pop 
CERN, CN Division
Email: dan...@cernapo.cern.ch
Mail:  CERN - PPE, Bat. 31 R-004, CH-1211 Geneve 23, Switzerland

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From: w...@netcom.com (William J. Evans)
Subject: Re: When Does Daylight Savings Time Change?
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<CvMAsJ.94r@news.cern.ch>
Date: Mon, 5 Sep 1994 14:47:55 GMT
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Dan Pop (dan...@cernapo.cern.ch) wrote:
: And in Europe it's the last Sunday in March and the last Sunday in
: September, at midnight (0:00am --> 1:00am and 1:00am --> 0:00am).

Are there any countries in Europe or the Middle East which either do
not have Daylight Savings Time (rather like the countries of Arizona
and Indiana) or which use a different convention?

-- Bill Evans

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From: lo...@ismennt.is (Logi Ragnarsson)
Newsgroups: comp.lang.c
Subject: Re: When Does Daylight Savings Time Change?
Date: 5 Sep 1994 22:42:35 -0000
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w...@netcom.com (William J. Evans) writes:

>Dan Pop (dan...@cernapo.cern.ch) wrote:
>: And in Europe it's the last Sunday in March and the last Sunday in
>: September, at midnight (0:00am --> 1:00am and 1:00am --> 0:00am).

>Are there any countries in Europe or the Middle East which either do
>not have Daylight Savings Time (rather like the countries of Arizona
>and Indiana) or which use a different convention?

Well, there is no daylight savings time in Iceland, and I would assume
some other places would not bother about it. There is little point this
far north.

Logi  -  lo...@ismennt.is

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From: ken...@cs.utwente.nl (Arjan Kenter)
Subject: Re: When Does Daylight Savings Time Change?
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<CvMAsJ.94r@news.cern.ch> <wjeCvnvrw.IBF@netcom.com> <34g6sr$2nn@rvik.ismennt.is>
Date: Tue, 6 Sep 1994 08:31:02 GMT
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In article <34g6sr$...@rvik.ismennt.is>, lo...@ismennt.is (Logi Ragnarsson) 
writes:
> w...@netcom.com (William J. Evans) writes:
> 
> >Dan Pop (dan...@cernapo.cern.ch) wrote:
> >: And in Europe it's the last Sunday in March and the last Sunday in
> >: September, at midnight (0:00am --> 1:00am and 1:00am --> 0:00am).
> 
> >Are there any countries in Europe or the Middle East which either do
> >not have Daylight Savings Time (rather like the countries of Arizona
> >and Indiana) or which use a different convention?
> 
> Well, there is no daylight savings time in Iceland, and I would assume
> some other places would not bother about it. There is little point this
> far north.

Also in Israel (maybe the rest of the Middle East too? Don't know) they have
another day. I remember the day I started my internship at the Technion in
Haifa, Israel, DST ended. Unfortunately, nobody had told me about it, so I
wondered why come it was so quiet on the university campus and why my
supervisor was late. He showed up an hour late! And when I asked him, he
replied like "Why? It's nine o'clock," when it was ten at my wristwatch...
This was the last Sunday of August '90 if I remember correctly (Sunday is
a working day in Israel).

-- 
                                       ^^
ir. H.J.H.N. Kenter                   oo )         ken...@cs.utwente.nl
University of Twente                 =x=  \        tel. +31 53 893747
Tele-Informatics & Open Systems        |   \       tfx. +31 53 333815
P.O. Box 217   7500 AE Enschede       /|__  \
The Netherlands                      (____)_/

As long as the answer is right, who cares if the question is wrong?

I never saw this cookie so I may not agree with it!

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From: to...@elf.bsdi.com (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: When Does Daylight Savings Time Change?
Date: 6 Sep 1994 07:37:26 -0700
Organization: Berkeley Software Design, Inc.
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In article <Cvp8zr....@cs.utwente.nl> Arjan Kenter <ken...@cs.utwente.nl>
writes:
>Also in Israel ... they have another day.

The rules for Israel, like those for just about everywhere on the
earth, are available in the Arthur Olson time zone package (available
as part of all current BSDs, including the 4.4-lite, FreeBSD, and
NetBSD).  Here is an excerpt from the `asia' table.

# Israel

# From U. S. Naval Observatory (January 19, 1989):
# ISRAEL              2 H  AHEAD OF UTC
# ISRAEL              3 H  AHEAD OF UTC  APR 10 - SEP 3

# From Ephraim Silverberg (April 18, 1989):

# Prior to 1989, the rules concerning Daylight Savings Time changed every
# year; as information, regarding exact times and dates during this period,
# is not readily available at the present time, the rules commence starting
# with the year 1989.

# From 1989 onwards the rules are as follows:
#
# 1. Daylight Savings Time commences midnight of the first Saturday night
#    following the seven-day festival of Pesach (Passover).  The transition
#    is from midnight Israel Standard Time to 1 a.m. Israel Daylight Savings
#    time.  As the Pesach festival is dependent on the Lunar calendar (the
#    first day is always on the 15th day of the month of Nisan), the rule
#    changes every year on the Gregorian calendar.
#
# 2. Standard Time is reinstated on the Saturday night whereupon Jews
#    following the Ashkenazi (European) rite begin to recite the Selichot
#    (forgiveness) prayers prior to the Jewish Lunar New Year.  The transition
#    is from midnight Israel Daylight Savings time to 11 p.m. Israel Standard
#    Time.  The law (according to the Ashkenazi custom) concerning the
#    commencement of the Selichot prayers is described in chapter 128, section
#    5 of the "Code of Jewish Law," by Rabbi Shlomo Ganzfried (translated by
#    Hyman E. Goldin):
#
#       Beginning with the Sunday [**] before Rosh Hashanah [***],
#       we rise early for the service of Selichot (supplications for
#       forgiveness).  If Rosh Hashanah occurs on Monday or Tuesday, we
#       begin saying the Selichot from the Sunday of the preceding week.
#
#    This, too, varies from year to year on the Gregorian calendar and, thus,
#    two explicit timezone rules are required for each Gregorian year.
#
#    [**] actually Saturday night as the Jewish day commences at nightfall.
#    [***] the Jewish Lunar New Year.

# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
Rule	Zion	1989	only	-	Apr	30	0:00	1:00	D
Rule	Zion	1989	only	-	Sep	24	0:00	0:00	S
Rule	Zion	1990	only	-	Apr	22	0:00	1:00	D
Rule	Zion	1990	only	-	Sep	16	0:00	0:00	S
Rule	Zion	1991	only	-	Apr	 7	0:00	1:00	D
Rule	Zion	1991	only	-	Sep	 1	0:00	0:00	S
Rule	Zion	1992	only	-	Apr	26	0:00	1:00	D
Rule	Zion	1992	only	-	Sep	20	0:00	0:00	S
Rule	Zion	1993	only	-	Apr	18	0:00	1:00	D
Rule	Zion	1993	only	-	Sep	12	0:00	0:00	S
Rule	Zion	1994	only	-	Apr	 3	0:00	1:00	D
Rule	Zion	1994	only	-	Aug	28	0:00	0:00	S
Rule	Zion	1995	only	-	Apr	23	0:00	1:00	D
Rule	Zion	1995	only	-	Sep	17	0:00	0:00	S
Rule	Zion	1996	only	-	Apr	14	0:00	1:00	D
Rule	Zion	1996	only	-	Sep	 8	0:00	0:00	S
Rule	Zion	1997	only	-	May	 4	0:00	1:00	D
Rule	Zion	1997	only	-	Sep	28	0:00	0:00	S
Rule	Zion	1998	only	-	Apr	19	0:00	1:00	D
Rule	Zion	1998	only	-	Sep	13	0:00	0:00	S
Rule	Zion	1999	only	-	Apr	11	0:00	1:00	D
Rule	Zion	1999	only	-	Sep	 5	0:00	0:00	S
Rule	Zion	2000	only	-	Apr	30	0:00	1:00	D
Rule	Zion	2000	only	-	Sep	24	0:00	0:00	S
Rule	Zion	2001	only	-	Apr	15	0:00	1:00	D
Rule	Zion	2001	only	-	Sep	 9	0:00	0:00	S
Rule	Zion	2002	only	-	Apr	 7	0:00	1:00	D
Rule	Zion	2002	only	-	Sep	 1	0:00	0:00	S
Rule	Zion	2003	only	-	Apr	27	0:00	1:00	D
Rule	Zion	2003	only	-	Sep	21	0:00	0:00	S
Rule	Zion	2004	only	-	Apr	18	0:00	1:00	D
Rule	Zion	2004	only	-	Sep	12	0:00	0:00	S
Rule	Zion	2005	only	-	May	 1	0:00	1:00	D
Rule	Zion	2005	only	-	Sep	25	0:00	0:00	S
Rule	Zion	2006	only	-	Apr	23	0:00	1:00	D
Rule	Zion	2006	only	-	Sep	17	0:00	0:00	S
Rule	Zion	2007	only	-	Apr	15	0:00	1:00	D
Rule	Zion	2007	only	-	Sep	 9	0:00	0:00	S
Rule	Zion	2008	only	-	Apr	27	0:00	1:00	D
Rule	Zion	2008	only	-	Sep	21	0:00	0:00	S
Rule	Zion	2009	only	-	Apr	19	0:00	1:00	D
Rule	Zion	2009	only	-	Sep	13	0:00	0:00	S

# Zone	NAME		GMTOFF	RULES/SAVE	FORMAT	[UNTIL]
Zone	Israel		2:00	Zion		I%sT

# The following is a chart of the day of the week and Gregorian date of
# the first day of Pesach and the first day of Rosh Hashanah for the years
# 1989 through 2009 inclusive.
#
# First Day of Passover
# ---------------------
# Gregorian Year	Day of Week	Month		Day
# --------------	-----------	-----		---
#	1989		Thursday	April		20
#	1990		Tuesday		April		10
#	1991		Saturday	March		30
#	1992		Saturday	April		18
#	1993		Tuesday		April		 6
#	1994		Sunday		March		27
#	1995		Saturday	April		15
#	1996		Thursday	April		 4
#	1997		Tuesday		April		22
#	1998		Saturday	April		11
#	1999		Thursday	April		 1
#	2000		Thursday	April		20
#	2001		Sunday		April		 8
#	2002		Thursday	March		28
#	2003		Thursday	April		17
#	2004		Tuesday		April		 6
#	2005		Sunday		April		24
#	2006		Thursday	April		13
#	2007		Tuesday		April		 3
#	2008		Sunday		April		20
#	2009		Thursday	April		 9
#
# First Day of Rosh Hashanah
# --------------------------
# Gregorian Year	Day of Week	Month		Day
# --------------	-----------	-----		---
#	1989		Saturday	September	30
#	1990		Thursday	September	20
#	1991		Monday		September	 9
#	1992		Monday		September	28
#	1993		Thursday	September	16
#	1994		Tuesday		September	 6
#	1995		Monday		September	25
#	1996		Saturday	September	14
#	1997		Thursday	October		 2
#	1998		Monday		September	21
#	1999		Saturday	September	11
#	2000		Saturday	September	30
#	2001		Tuesday		September	18
#	2002		Saturday	September	 7
#	2003		Saturday	September	27
#	2004		Thursday	September	16
#	2005		Tuesday		October		 4
#	2006		Saturday	September	23
#	2007		Thursday	September	13
#	2008		Tuesday		September	30
#	2009		Saturday	September	19
-- 
In-Real-Life: Chris Torek, Berkeley Software Design Inc
Berkeley, CA	Domain:	to...@bsdi.com	+1 510 549 1145

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eggert
From: egg...@twinsun.com (Paul Eggert)
Subject: Re: When Does Daylight Savings Time Change?
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<34g6sr$2nn@rvik.ismennt.is> <Cvp8zr.E9t@cs.utwente.nl> <34hur6$qvb@elf.bsdi.com>
Date: Fri, 16 Sep 1994 17:27:19 GMT
Lines: 24

to...@elf.bsdi.com (Chris Torek) writes:

> The rules for Israel, like those for just about everywhere on the
> earth, are available in the Arthur Olson time zone package (available
> as part of all current BSDs, including the 4.4-lite, FreeBSD, and
> NetBSD).  Here is an excerpt from the `asia' table.

Alas, that April 1989 excerpt is woefully out of date -- Israel changes
time zone rules more often than it changes governments, and by
September 1989 they had already changed the rules again.
Whatever BSD you got it from should update its tables
from the latest version in elsie.nci.nih.gov in pub/tz*.

Time zone rules are intensely political in Israel -- e.g. I've heard
that in the occupied territories the resistance used time zone rules
that differed from the government's, and I don't know what the new
Palestinian government is doing about this.  It would be nice to send
future corrections to the email address given in the tables.

I strongly second the suggestion of using mktime() and the tz package
to answer questions like ``when does daylight savings time change?''.
Why reinvent the wheel?  The tz package even comes with a program
`zdump' that answers this very question, and its source code is
portable and is in the public domain.




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