Subject: Re: bug#16663: emacs/calc/date

From: Jay Belanger <[email-masked]>
Date: Thu, 06 Feb 2014 22:52:42 -0600

Steve Allen <[email-masked]> writes:
...
> The notion of daylight saving time in the 17th century should be a
> clue that some underlying concept here is very wrong in the calendar
> model.

For daylight savings time calculation, Calc only differentiates between
before/after 2007.  I think Calendar might do the same.  I don't know
about Calendar, but by default Calc bases its DST adjustments based on the time
zone and whether or not daylight savings time is used at all.  (Each
person could write their own DST function, but that would be a pain.)
I don't know whether or not anything too much more sophisticated can be
done, but I'll look into it after the next Emacs release.  (Perhaps
something like a user configurable "DST begins this year" and "DST ends
this year"; as far as I can tell, the beginning and end years depend on
more than the time zone.)

> In this and many other cases of computed proleptic dates the only
> reasonable interpretation of the time scale is Universal Time (UT, not
> UTC).

Could you be more precise?  From what I've read, UT isn't precisely
defined and UTC is one possible interpretation of it.

Thanks,
Jay