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

Paul Eggert eggert at
Sat Jan 21 05:56:23 UTC 2006

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 this:

   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 transition:

   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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