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Re: cal-persia.el disagrees with Iranian calendar in A.D. 2025

From: Ed Reingold
Subject: Re: cal-persia.el disagrees with Iranian calendar in A.D. 2025
Date: Thu, 31 Mar 2005 08:39:38 -0600

> 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  <address@hidden>
>       * 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

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