Re: The Emacs Calculator and calendar

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

On 10/06/2012 08:49 PM, Richard Stallman wrote:

> all of Europe used the Julian calendar for hundreds of years.

Unfortunately that's not correct, if by "Julian calendar"
one means the Julian calendar that Emacs implements.  (In
this email I'll call it the "Emacs Julian calendar", to
clearly distinguish it from the many other Julian calendars.)

For example, England never used the Emacs Julian calendar:
before 1752, English years started on March 25, and after
1752 England used Gregorian.  The Holy Roman Empire used the
Emacs Julian calendar for only four decades, from 1544 to
1582.  Other European countries used the Emacs Julian
calendar for a bit longer in some cases, but off the top of
my head I can think of only one country that actually used
the Emacs Julian calendar for hundreds of years, namely
Russia from 1700 through 1918.

> Jan 5, 1000 in the Gregorian calendar was Dec 31, 999
> in the Julian calendar.

It's true that nobody called it "Jan 5, 1000" back then,
because the Gregorian calendar wasn't invented yet.  But
it's also true that very few people called it "December 31,
999" back then, because the Emacs-style Julian calendar was
pretty rare, perhaps even nonexistent, back then.  So both
calendars are being used proleptically (i.e., extrapolating
them backward into the past) if we are talking about that
date.

> If something happened in Europe on that day, which year
> do modern historians say it occurred in?

Most modern European historians would probably say 999.
But for the date 30 days later, some would say 999,
others 1000, and still others 999/1000.

Old dates are a real mess.  This may help to explain why Ed
Reingold worded his advice so strongly.  The method of Unix
cal and Emacs calc looks cute, but it's incorrect in the
sense that it doesn't correspond to any actual historical
practice, so it arguably causes more harm (by confusing
users) than it cures.  The method of Emacs calendar is much
saner.