Question on interpretation of rules intervals

Olson, Arthur David (NIH/NCI) [E] olsona at
Mon Apr 2 14:26:28 UTC 2007

Starting in 1942, the U.S. observed Daylight Saving Time year-round as
part of a war-time effort to conserve energy; rather than being called
"Standard" or "Daylight" time, it was called "War" time (as in "Eastern
War Time").

WWII ended during the summer of 1945, when Daylight Saving Time would
normally be observed; folks started using "Peace" rather than "War" in
time zone names (such as "Eastern Peace Time").

When the normal "fall back" date arrived in 1945, folks reverted to
"Eastern Standard Time" (and to "Eastern Daylight Time" in 1946).

So...there's one rule in 1942 to get things on to "War" time (in effect
through 1945, with no clock changes), one rule in 1945 to get things on
to "Peace" time, and one rule in 1945 to "fall back" to standard time.


-----Original Message-----
From: Liviu Nicoara [mailto:nicoara at] 
Sent: Monday, April 02, 2007 10:17 AM
To: tz at
Subject: Question on interpretation of rules intervals

Hi all,

I have a question about how to interpret the US set of rules. After 
going through the "zic" man page and the mailing list archive I am still

unclear about the meaning of using this:

Rule US 1942 only - Feb  9 2:00   1:00 W # War
Rule US 1945 only - Aug 14 23:00u 1:00 P # Peace
Rule US 1945 only - Sep 30 2:00      0 S

in a zone definition like this:

Zone America/New_York -4:56:02 -  LMT  1883 Nov 18 12:03:58
                       -5:00   US  E%sT 1920
                       -5:00   NYC E%sT 1942
                       -5:00   US  E%sT 1946

As I see it, the US rule has a transition in 1942 (only), on Feb 9th, 
where it saved 1 hour. Am I correct in interpreting the gap of 43-44 as:

1. The transition of 1942 was observed up until 1945, Sep 30th, and...
2. The entry for Aug 14th, 1945 transition exists only in order to be
    used in time zones which did not observe the 1942 transition?


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