On Sat 2015-03-07T14:14:07 -0500, Brooks Harris hath writ: > It is typically warned that date and time before 1972 cannot be > accurately represented with NTP or POSIX, for examples.
I would say that for PTP * all seconds are always SI seconds * seconds after 1972-01-01 correspond to (TAI - 10) * seconds before 1972-01-01 do not align with civil time * in particular, 1970-01-01 in PTP does not correspond to any event in any time scale which was then in use, but that does not matter For PTP it is the uniformity going forward that is the goal. I would say that the intent NTP and POSIX is to correspond to civil time in contemporary use. Therefore, for dates before 1972-01-01 NTP and POSIX are counting seconds of UT. For dates after 1972-01-01 I would say that NTP and POSIX are both confused about whether they are counting SI seconds or UT days. Therein, of course, lies the basis of this LEAPSECS list. I see it as inevitable that the confusion must end, therefore NTP and POSIX will eventually be unambiguous that they are counting SI seconds. That means that, eventually, any general purpose time scale intended to correspond to civil time will be a piecewise continuous time scale. Such general purpose time scales will have a date at which they switch from counting UT days to counting SI seconds. Deciding on that date, and how it will be implemented and understood, is what we hope the ITU-R will accomplish at WRC-15. > For date-time before 1972 you've got to switch to some > other timescale depending on the purpose at hand. Exactly so. Before 1972 civil time was not SI seconds. -- Steve Allen <s...@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
