[tz] isdst bug Europe/Dublin (tzdb-2019c)

[Michael H Deckers]

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
        2000-01-01,
        JD 2451 544.5
        MJD 40 587 + 946 684 800 s
        -50 a B.P.
    all denote the same point on the time axis.

    Michael Deckers.