From: Ketil Malde [mailto:ketil+haskell@ii.uib.no]
I don't think this is correct. In UTC, extra leap seconds are denoted 23:59:60 and the missing ones have :59:58 as the last second. Posix's seconds are thus not isomorphic to UTC.
Ahh, yes, sorry: http://cr.yp.to/proto/utctai.html http://tycho.usno.navy.mil/systime.html http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm I should read more... So UTC and UT1 seem to be more-or-less equivalent, in that they both include leap seconds. UT1 measures the actual earth day (so I assume it has some fractional component for seconds), while UTC (which I assume counts integral seconds) tracks UT1 with an error of +/-0.9s. UTC "differs from TAI by an integral number of seconds". TAI ignores leap seconds, but does track time accurately by always ticking (i.e. not slowing down at a leap second). There are exactly 86400 seconds in a TAI day, so the day will drift w.r.t. the earth's actual day, whereas UTC tracks the actual day accurately by inserting leap seconds. So the TAI day isn't very useful. POSIX is "idealised" time, where days are always 23:59:59, and a second sometimes takes two seconds. Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************