Steve Allen via tz <tz@iana.org> wrote:
Thanks for your thoughts, Steve! They are always appreciated.
It is much simpler to ignore the 50 to 200 ms jumps that were put into old UTC and say that before 1972 all available sources of civil time provided UT (nevermind the particular flavor, nobody set their clock that accurately) and after 1972 UTC with leap seconds.
For civil time I do not see any advantage in a model with greater complexity than just plain UT as the basis time scale before 1972-01-01. This is adequate for any IANA tz library.
That's effectively what the PTP and tz "right" timescales do: before 1972 they are unspecified UT. Which is probably fine, but I would like a better idea of what people want from an atomic or uniform time counter that operates alongside POSIX. But PTP has a mismatch with DTAI: POSIX - PTP == TAI - UTC - 10, so it would be deeply confusing to associate a PTP-like timescale with the name "TAI" (as well as upsetting to the IERS / BIPM). A couple of other motivations for my old proleptic UTC idea: I wanted the correct values for DTAI after 1972, so you could plug a broken-down TAI time into the POSIX formula and get the correct timestamp. And I didn't want to pretend to be accurate to better than about one second before 1972; I think it's preferable to be overtly ahistorical than to claim a precision that isn't possible. Tony. -- f.anthony.n.finch <dot@dotat.at> https://dotat.at/ Shannon, Rockall, Malin: North 4 to 6 veering northeast 5 to 7. Moderate or rough. Showers. Good.