Re: The Emacs Calculator and calendar

[Paul Eggert <eggert@cs.ucla.edu>]

On 10/06/2012 08:41 AM, Richard Stallman wrote:

> Nobody used the Gregorian calendar in 1400,
> so displaying dates from that year in Gregorian is an anachronism.

It's OK and common to use an anachronism.  It is standard
practice to use modern calendars when talking about old dates.
Almost nobody who writes about ancient history specifies dates in the
calendars that were used at the time.  Instead, people typically use a
more-modern calendar, and write things like "Caesar was assassinated
in 44 BC" or "Wu became emperor of all China in 280".

It's true that it's also common practice to use the Julian calendar
when talking about events that occurred before 1752 in British-contolled
territory, and to use the Gregorian calendar for later events in that
territory.  But this is a special case, and it does not generalize well
elsewhere.

> Perhaps a calendar program should allow the user to specify changeover
> date, offering convenient options for the main jurisdictions of interest.

Unfortunately there are thousands of jurisdictions, and
there is no systematic database of this stuff that I know of.
Some places switched back and forth several times, and the
switchover dates are not always known.  In some locations,
both calendars were used simultaneously, and whether
you used Julian or Gregorian dates depended on what reason
you wanted the dates.  (A few places *still* use Julian
for some official purposes.)  And things get even more
complicated once one considers all the other calendars that are
or have been in practical use.  So I'm afraid this suggestion,
though appealing in principle, is not practical.