[tz] isdst bug Europe/Dublin (tzdb-2019c)
Michael H Deckers
michael.h.deckers at googlemail.com
Mon Dec 16 13:43:56 UTC 2019
On 2019-12-16 03:57, Guy Harris wrote:
> On Dec 15, 2019, at 5:22 AM, Michael H Deckers <michael.h.deckers at googlemail.com> wrote:
>> The notation of values of TAI using the Gregorian calendar is helpful
>> when comparing time scales.
> So how is that defined?
> Do you just take a UTC value for the same instant, add the current TAI - UTC delta to it - and, for overflow (meaning "resulting seconds > 59 or minutes > 59 or...), "carry into" the calendar date, so that an event that took place at the end of 2018, with a UTC label, took place at the beginning of 2019, with a TAI label?
Yes. If TAI was 1977-01-01, then TAI - UTC was 15 s, so that
UTC was 1977-01-01 - 15 s = 1976-12-31T23:59:45.
A calendar date just denotes a point on the time axis; and
a time scale assigns a point on the time axis to each point
of a region of spacetime (on which the time scale is defined).
That is a "time scale" in the astronomical sense of the word,
where TCB, TCG, TDB, TT, UTC, UT1, UT2, and local civil times
are time scales. A "geological time scale" is something else;
IEC 60050 has additional meanings for "time scale".
A calendar is not restricted to the notation of values of one
specific time scale, and points on the time axis can also be
denoted by other means: the notations
JD 2451 544.5
MJD 40 587 + 946 684 800 s
-50 a B.P.
all denote the same point on the time axis.
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