On Sun 2014-01-19T23:53:44 +0000, Zefram hath writ: > I'm not familiar with PTP, but I see a number of documents saying that it > uses an epoch of 1970-01-01 00:00:00 TAI. If so, unlike the NTP origin > this is a perfectly well-defined real instant.
Yes, well-defined, but not defined in a contemporary sense that any such time stamps could have existed. Anything with that stamp was reconstructed ex post facto. The CCDS meeting which produced the definition for TAI was held 1970-06-18/19. After that got to the CIPM that became known as Recommendation S 2 (CCDS, 1970), in CIPM, 1970 The CGPM meeting which authorized the existence of TAI was opened 1971-10-04 in Resolutions 1 and 2. This is a perennial problem in metrology of things that progress. If a precise definition is desired for a coordinate origin then that origin must be expressed in measures of the current conventional value with current technologies. The past of POSIX time stamps can never be disambiguated without argument. If it becomes possible to choose a new time scale with which everyone can live then the POSIX standard will have to specify a new conventional date at which time_t has a new conventional count of 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 http://six.pairlist.net/mailman/listinfo/leapsecs
