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 <http://www.twinsun.com/tz/tz-link.htm>. 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 <http://dmses.dot.gov/docimages/pdf95/382329_web.pdf>. 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@elsie.nci.nih.gov>. Thanks. Sincerely, Paul Eggert Computer Science Dept. 4532J Boelter Hall University of California Los Angeles, CA 90095-1596 +1 310 267 2254 (voice) eggert@ucla.edu (email)