off-by-one-hour error in OST Docket No. 2005-22114

Paul Schauble Paul.Schauble at
Mon Jan 23 14:03:37 UTC 2006

Doesn't the first proposal have the problem that there is no 2:59:59 EST,
the Eastern zone having changed to DST?


-----Original Message-----
From: tz-request at [mailto:tz-request at] On
Behalf Of Paul Eggert
Sent: Friday, January 20, 2006 10:56 PM
To: Judith S. Kaleta
Cc: Time zone mailing list
Subject: off-by-one-hour error in OST Docket No. 2005-22114

Judith S. Kaleta
Office of the General Counsel
US Dept. of Transportation
Room 10428
400 Seventh St
Washington, DC 20590

Dear Ms. Kaleta:

I help maintain the public-domain tz database of time zone and daylight
saving time transitions.  This database contains code and data that
represent the history of local time, and is used by many computers around
the world.  For details, please see <>.
Needless to say, we've been following the Indiana situation with interest.

Deborah Goldsmith of Apple Computer, one of our correspondents, recently
noted what appears to be a one-hour error in docket
OST-2005-22114 <>.

Quoting from the first page of that document:

   DATES: The effective date of this rule is 2:00 a.m. EST Sunday,
   April 2, 2006, which is the changeover date from standard time to
   Daylight Saving Time.

This cannot be exactly what was intended, because 2:00 a.m. EST corresponds
to 1:00 a.m. CST, at which point clocks in the Central time zone will not
spring forward for another hour.  Therefore, as written, the rule requires
that a clock in the affected area must jump backwards from 02:00 EST to
01:00 CST, and then an hour later jump ahead from 02:00 CST to 03:00 CDT.
In other words, the currently-required clock transitions would look like

   01:59:59 EST
   ... and then, one second later,...
   01:00:00 CST
   ... and then, one hour later,...
   01:59:59 CST
   ... and then, one second later,...
   03:00:00 CDT

We doubt whether you really intended that the citizens of Vincennes, Indiana
should stay up in the middle of the night and change their clocks twice.

Our correspondents have suggested two different ways out of this problem.
First, and perhaps simplest, you could change the effective time of the rule
from 2:00 a.m. EST to 3:00 a.m. EST.  This will result in the following

   02:59:59 EST
   ... and then, one second later,...
   03:00:00 CDT

Second, if you prefer sticking to a 2:00 a.m. transition, you could append
the following sentences:

   Counties that move from the Eastern to the Central Time Zone will
   switch directly from EST to CDT, so that their clocks need not
   change.  From 2:00 a.m. CDT to 3:00 a.m. CDT these clocks will use
   CDT even though the rest of the Central Time Zone will still be
   using CST.
This would result in the following transition:

   01:59:59 EST
   ... and then, one second later,...
   02:00:00 CDT

Please let us know which solution (if any) you prefer, by writing to us in
the time zone mailing list <tz at>.  Thanks.


Paul Eggert
Computer Science Dept.
4532J Boelter Hall
University of California
Los Angeles, CA 90095-1596
+1 310 267 2254 (voice)
eggert at (email)

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