From d95deb6744bc45274a533c6028ff9f0bad281627 Mon Sep 17 00:00:00 2001 From: Jay Belanger Date: Mon, 19 Mar 2007 03:36:17 +0000 Subject: [PATCH] (Time Zones): Mention the 2007 rule change. --- man/calc.texi | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/man/calc.texi b/man/calc.texi index d927346ff6b..0544bc1e3b4 100644 --- a/man/calc.texi +++ b/man/calc.texi @@ -17379,9 +17379,10 @@ commands. In particular, @samp{ - } evaluates to exactly 30 days even though there is a daylight-saving transition in between. This is also true for Julian pure dates: @samp{julian() - julian()}. But Julian -and Unix date/times will adjust for daylight saving time: +and Unix date/times will adjust for daylight saving time: using Calc's +default daylight saving time rule (see the explanation below), @samp{julian(<12am may 1 1991>) - julian(<12am apr 1 1991>)} -evaluates to @samp{29.95834} (that's 29 days and 23 hours) +evaluates to @samp{29.95833} (that's 29 days and 23 hours) because one hour was lost when daylight saving commenced on April 7, 1991. @@ -17501,12 +17502,15 @@ non-daylight-saving time. @vindex math-daylight-savings-hook @findex math-std-daylight-savings By default Calc always considers daylight saving time to begin at -2 a.m.@: on the second Sunday of March, and to end at 2 a.m.@: on the -first Sunday of November. This is the rule that has been in effect -in North America since 2007. If you are in a country that uses -different rules for computing daylight saving time, you have two -choices: Write your own daylight saving hook, or control time -zones explicitly by setting the @code{TimeZone} variable and/or +2 a.m.@: on the second Sunday of March (for years from 2007 on) or on +the last Sunday in April (for years before 2007), and to end at 2 a.m.@: +on the first Sunday of November. (for years from 2007 on) or the last +Sunday in October (for years before 2007). These are the rules that have +been in effect in much of North America since 1966 and takes into +account the rule change that began in 2007. If you are in a +country that uses different rules for computing daylight saving time, +you have two choices: Write your own daylight saving hook, or control +time zones explicitly by setting the @code{TimeZone} variable and/or always giving a time-zone argument for the conversion functions. The Lisp variable @code{math-daylight-savings-hook} holds the -- 2.39.5