[tz] JavaScript IANA date/time library, now with support for leap seconds, TAI, TDT

[Tony Finch]

Steve Allen via tz <tz at 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.
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