It mentions the March 20, 2025 discrepancy, and it has some interesting and not-altogether-positive things to say about the method used in GNU Emacs. I hadn't realized how controversial this area is.

Had I realized how controversial it was, I would not have included it in Emacs, I only learned that is 1998, long after the code was released. Still, it is not a bad approximation, but it should be labeled as such.

Thanks for clarifying this. Would it be appropriate to make the following change to the GNU Emacs user documentation, if only to help forestall future bug reports in this area?

Your change (below) is fine.

2005-03-31 Paul Eggert <eggert@cs.ucla.edu>

* calendar.texi (Calendar Systems): Mention that the Persian calendar implemented is the arithmetical calendar of Birashk.

--- calendar.texi.~1.33.~ 2005-03-28 16:30:06 -0500 +++ calendar.texi 2005-03-31 01:46:45 -0500 @@ -691,6 +691,12 @@ Their calendar consists of twelve months days, the next five have 30 days, and the last has 29 in ordinary years and 30 in leap years. Leap years occur in a complicated pattern every four or five years. +The calendar implemented here is the arithmetical Persian calendar +championed by Birashk, based on a 2,820-year cycle. It differs from +the astronomical Persian calendar, which is based on astronomical +events. As of this writing the first future discrepancy is projected +to occur on March 20, 2025. It is currently not clear what the +official calendar of Iran will be that far into the future.

@cindex Chinese calendar The Chinese calendar is a complicated system of lunar months arranged