I've gleened from this thread that: * everyone uses UTC, or should, because UTC is a uniform time scale, except for those leap seconds * UTC is sourced from the frequence of a radio emission from cesium atoms which are extremely constant * UTC can get out of whack with the rotation of the earth around the sun, because our rotation is not uniform, but is calculated rather than measured (well, sort of) * UTC is TAI plus leap seconds. In 1972, when leap seconds were first introduced, UTC was TAI - 10 seconds. UTC is now TAI - 34 seconds. TAI ticks exactly as fast as UTC, ignoring leap second adjustments. * UTC is slower than UT1 by about 1ms per day. * On 12/31/2008 UTC was (-) 591.8ms behind UT1. On 1/1/2008 UTC was 407.1ms ahead of UT1. * Leap seconds are applied to UTC every few years to remain in line with UT1, the time based on the rotation of the earth around the sun. * GMT is used to imply UT1, but sometimes UTC, but really GMT is just massively confusing and you shouldn't use it, either in conversation or in your servers/routers, because nobody is really sure without reading a lot of documentation what GMT means for each manufacturer/OS/software. * When writing code regarding dates and times, know that any year may have 366 days, and any minute may have 61 seconds. * When in doubt, Dr. Daniel Gambis is always right. Beckman On Mon, 5 Jan 2009, Marshall Eubanks wrote:
Having been involved in the leap second business, I can tell you that Daniel Gambis strictly follows the rules, which are Bulletin C is mailed every six months, either to announce a time step in UTC or to confirm that there will be no time step at the next possible date.
--------------------------------------------------------------------------- Peter Beckman Internet Guy beckman@angryox.com http://www.angryox.com/ ---------------------------------------------------------------------------