Variable: calc-gregorian-switch

calc-gregorian-switch is a customizable variable defined in calc.el.gz.

Value

nil

Documentation

The first day the Gregorian calendar is used by Calc's date forms.

This is nil (the default) if the Gregorian calendar is the only one used. Otherwise, it should be a list (YEAR MONTH DAY) when Calc begins to use the Gregorian calendar; Calc will use the Julian calendar for earlier dates. The dates in which different regions of the world began to use the Gregorian calendar vary quite a bit, even within a single country. If you want Calc's date forms to switch between the Julian and Gregorian calendar, you can specify the date or choose from several common choices. Some of these choices should be taken with a grain of salt; for example different parts of France changed calendars at different times, and Sweden's change to the Gregorian calendar was complicated. Also, the boundaries of the countries were different at the times of the calendar changes than they are now. The Vatican decided that the Gregorian calendar should take effect on 15 October 1582 (Gregorian), and many Catholic countries made the change then. Great Britain and its colonies had the Gregorian calendar take effect on 14 September 1752 (Gregorian); this includes the United States.

This variable was added, or its default value changed, in Emacs 24.4.

Probably introduced at or before Emacs version 24.4.

Source Code

;; Defined in /usr/src/emacs/lisp/calc/calc.el.gz
;; Dates that are built-in options for `calc-gregorian-switch' should be
;; (YEAR MONTH DAY math-date-from-gregorian-dt(YEAR MONTH DAY)) for speed.
(defcustom calc-gregorian-switch nil
  "The first day the Gregorian calendar is used by Calc's date forms.
This is nil (the default) if the Gregorian calendar is the only one used.
Otherwise, it should be a list `(YEAR MONTH DAY)' when Calc begins to use
the Gregorian calendar; Calc will use the Julian calendar for earlier dates.
The dates in which different regions of the world began to use the
Gregorian calendar vary quite a bit, even within a single country.
If you want Calc's date forms to switch between the Julian and
Gregorian calendar, you can specify the date or choose from several
common choices.  Some of these choices should be taken with a grain
of salt; for example different parts of France changed calendars at
different times, and Sweden's change to the Gregorian calendar was
complicated.  Also, the boundaries of the countries were different at
the times of the calendar changes than they are now.
The Vatican decided that the Gregorian calendar should take effect
on 15 October 1582 (Gregorian), and many Catholic countries made
the change then.  Great Britain and its colonies had the Gregorian
calendar take effect on 14 September 1752 (Gregorian); this includes
the United States."
  :version "24.4"
  :type '(choice (const :tag "Always use the Gregorian calendar" nil)
                 (const :tag "1582-10-15 - Italy, Poland, Portugal, Spain" (1582 10 15 577736))
                 (const :tag "1582-12-20 - France" (1582 12 20 577802))
                 (const :tag "1582-12-25 - Luxemburg" (1582 12 25 577807))
                 (const :tag "1584-01-17 - Bohemia and Moravia" (1584 1 17 578195))
                 (const :tag "1587-11-01 - Hungary" (1587 11 1 579579))
                 (const :tag "1700-03-01 - Denmark" (1700 3 1 620607))
                 (const :tag "1701-01-12 - Protestant Switzerland" (1701 1 12 620924))
                 (const :tag "1752-09-14 - Great Britain and dominions" (1752 9 14 639797))
                 (const :tag "1753-03-01 - Sweden" (1753 3 1 639965))
                 (const :tag "1918-02-14 - Russia" (1918 2 14 700214))
                 (const :tag "1919-04-14 - Romania" (1919 4 14 700638))
                 (list :tag "(YEAR MONTH DAY)"
                       (integer :tag "Year")
                       (integer :tag "Month (integer)")
                       (integer :tag "Day")))
  :set (lambda (symbol value)
         (set-default symbol value)
         (setq math-format-date-cache nil)
         (calc-refresh)))