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bug#20583: calendar-absolute-from-gregorian

From: Nicholas Strauss
Subject: bug#20583: calendar-absolute-from-gregorian
Date: Fri, 15 May 2015 18:48:02 -0700

Hi Glenn,

The real point here is that Calendar Systems are instruments and as
subject are subject to error (Think like an engineer!). The real world
is messy -- Pope Gregory abolished some days, and various countries
took their time to jump on the band wagon.

I think what Reingold is/was trying to do was to use "absolute" as an
internal reference format -- a primary key -- that would correlate all the
other calendars.

there are other "absolute" choices for internal references.
Peter Duffett-Smith took a different approach -- he counts 2415020
days from January 1, 4713 BC until the 1900 epoch, January 0.5, 1900.

This crops up in sqlite3 calculations for date() and also common
javascript formulas.

I am still researching this.

If our civilization lasts for any appreciable time, having a consistent
calendar will be crucial for keeping a consistent history.
I think this helps why I am stressing the astronomy. If an Aztec calendar
records an eclipse on a certain day, that's pretty much it.


On Fri, May 15, 2015 at 5:54 PM, Glenn Morris <address@hidden> wrote:
> Nicholas Strauss wrote:
>> Why does (calendar-absolute-from-gregorian '(10 10 1582))
>> return 577731?
>> (calendar-generate '(10 1582)) is another example of this
>> error.
> It's behaving as designed. It's a utility function that operates on the
> basis that today's calendar system is valid for all time. It's not meant
> as literally historically accurate, and I think trying to make it so (by
> introducing discontinuities at certain dates) would be a mistake. See eg
> thread at:
> http://lists.gnu.org/archive/html/emacs-devel/2006-07/msg01008.html

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