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A perpetual calendar is a calendar valid for many years, usually designed to look up the day of the week for a given date in the past or future.
For the Gregorian and Julian calendars, a perpetual calendar typically consists of one of three general variations:
Such a perpetual calendar fails to indicate the dates of moveable feasts such as Easter, which are calculated based on a combination of events in the Tropical year and lunar cycles. These issues are dealt with in great detail in computus.
An early example of a perpetual calendar for practical use is found in the Nürnberger Handschrift GNM 3227a. The calendar covers the period of 1390–1495 (on which grounds the manuscript is dated to c. 1389). For each year of this period, it lists the number of weeks between Christmas day and Quinquagesima. This is the first known instance of a tabular form of perpetual calendar allowing the calculation of the moveable feasts that became popular during the 15th century.