[tz] Fwd: DST changes in Hungary (full historical revision)

[Michael H Deckers]

    On 2020-06-09 16:05, Paul Eggert wrote:

>
> ... I didn't see anything in the source about time-of-day for
> the transition, though. In cases like that we simply list the date. So for now I
> installed the attached proposed patch.


    Yes, I know: in such cases the zic default is taken, so that the time
    of day is supposed to jump from 00:00 to 23:43:40.

    But this is certainly not the way of how railway times were adjusted.
    Railway time was not produced by each station but was disseminated via
    time signals sent from a single observatory. These time synchronization
    signals were sent frequently (eg, every ten minutes or so) on a 
telegraph
    line to all the stations in order to make sure that they all had the 
same
    time -- and the "same" time at least to the minute is essential for 
the service.

    So the jump in railway time would most likely be realized by the 
omission
    of several time synchronization signals for a short while before the 
jump
    (to alert the service personnel that clocks needed adjustment), 
followed by
    the synchronization signals for the time scale after the jump. In 
other words,
    the jump would be from (some signals before) 00:16:20 to the first
    synchronization signal for the new scale, at 00:00 exactly.

    In all the cases where I could check the exact time of day of a switch
    to time zone time, this turned out to be the case -- except, of course,
    for Dublin on 1916-10-01 where British law said that the time had to 
jump
    from 03:00:00 to 02:25:21.1.

    I guess I just wanted to say that the default jump produced by zic
    is not necessarily a good guess of what really has happened (except
    possibly for Britain).

    Michael Deckers.