Question on interpretation of rules intervals

Andy Lipscomb AndyLipscomb at
Mon Apr 2 14:28:22 UTC 2007

-----Original Message-----
From: Liviu Nicoara [mailto:nicoara at] 
Sent: Mon 2 April 2007 10:17
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?


Part 1, correct. The New York zone remained on Eastern War Time (-4:00) for all of 1943 and 1944.
Part 2, that change did not change the actual offset, which remained -4. It only changed the letter used in the abbreviation (since the US was no longer at war). It was indeed meant to be applied in all places using the US rule.

More information about the tz mailing list