abstract
| - A calendar reform is any significant revision of a calendar system. The term is sometimes also used for mere proposals of new calendars and changeovers from one calendar system to another. Most calendars consist of several rules, any of which may be altered by a reform:
* The grouping of days of the year into months, weeks, or similar subdivisions, together with any days of the year not belonging to these subdivions.
* A Leap year rule, determining which years are leap years, and how each leap year differs from the other years (common years)
* The numbering of years, i.e. selection of the epoch and the issue of year zero.
* The start of the year (e.g. winter solstice, January 1, March 1, spring equinox, Easter), week (usually Sunday or Monday, sometimes Saturday) and day (midnight, sunrise, noon, sunset).
* The naming of months and weekdays, as well as other special dates and periods (e.g. leap day or intercalary day).
* Alignment with religious and economic cycles as well as regular, recurring astronomic phenomena.
* Literal notation of dates.
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