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Perpetual calendar
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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.
Illustration from 1881 U.S. Patent 248872, for a perpetual calendar paperweight. The upper section is rotated to reveal one of seven lists of years (splitting leap years) for which the seven calendars below apply.
Illustration from 1881 U.S. Patent 248872, for a perpetual calendar paperweight. The upper section is rotated to reveal one of seven lists of years (s
A 50-year "pocket calendar" that is adjusted by turning the dial to place the name of the month under the current year. One can then deduce the day of
A 50-year "pocket calendar" that is adjusted by turning the dial to place the name of the month under the current year. One can then deduce the day of the week or the date.
Breguet classique Grand complication perpetual calendar
Breguet classique Grand complication perpetual calendar
Perpetual calendar wristwatch by Patek Philippe
Perpetual calendar wristwatch by Patek Philippe
Doomsday rule
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The Doomsday rule, Doomsday algorithm or Doomsday method is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves
Perpetual calendar
…Determination of the day of the week – Methods to calculate the day of the week Doomsday rule – Way of calculating the day of the week of a given date Long Now Foundation – American nonprofit organization…
John Conway, inventor of the Doomsday algorithm
John Conway, inventor of the Doomsday algorithm