[tz] What's "right"?

Tony Finch dot at dotat.at
Mon Nov 16 22:48:15 UTC 2020

Guy Harris <gharris at sonic.net> wrote:
> So what documents indicate how UTC was implemented prior to 1972-01-01
> 00:00:00 UTC?

One example is the USNO TAI-UTC file which includes details of their
version of 1960s rubber second UTC. The server is currently unavailable
(undergoing modernization, they say) but you can find copies via


I don't know which other timekeeping agencies used the same formulae.

> And, for anybody who cares in that much detail about the definition of
> the Epoch, should 1970-01-01 00:00:00 UTC be interpreted as *literally*
> being 1970-01-01 00:00:00 UTC, or as 1970-01-01 00:00:00 "new UTC
> extended backwards",

Neither :-) POSIX (as you know) disclaims any relationship between struct
tm values and actual time of day, so the meaning of timestamps in that
range, or any other range for that matter, is "whatever flavour of UTC or
GMT or zulu time makes the most sense and is most convenient".

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Fair Isle: Southwest 6 to gale 8, becoming cyclonic 4 to 6. Rough or very
rough, becoming moderate or rough. Rain or showers. Good, occasionally poor.

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