Whats a Perpetual Calendar? How is it different from an Annual Calendar or Triple-Date?
A perpetual calendar is the most developed form of the simple date window on a typical watch. It keeps track of date, day-of-the-week, (sometimes weeks), months, year, leap years, and sometimes even centuries. Because of the relatively complex rules governing the Gregorian calendar, including the varying lengths of months, and leap years every four years, a typical perpetual calendar has wheels turning from several times per second (e.g. balance wheel) all the way to once every four years. Because of the complexity of the Gregorian calendar, some perpetual calendars will require an experienced watchmaker open the watch to make an adjustment at AD 2100, or later (assuming that an experienced watchmaker still exists then). Some less complex calendars are also available: • Semi-perpetual calendars (e.g. the Breitling Montbrilliant 1461), which requires an adjustment on leap year day only. • annual calendars (of which the Patek Philippe 5035 is an outstanding example), which only require a
