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(Time Zones): Mention the 2007 rule change.

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Jay Belanger 2007-03-19 03:36:17 +00:00
parent 96cd475f4b
commit d95deb6744
1 changed files with 12 additions and 8 deletions
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20
man/calc.texi
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@ -17379,9 +17379,10 @@ commands. In particular, @samp{<may 1 1991> - <apr 1 1991>} 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(<may 1 1991>) - julian(<apr 1 1991>)}. 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