Perpetual calendar

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Girard-Perregaux Vintage 1945 XXL Tourbillon
with perpetual calendar
© Girard-Perregaux

Watch function (also: eternal calendar, everlasting calendar; French: Quantième Perpétuel)

A complicated mechanism (complication) for large clocks and wristwatches, which displays the correct date of the Gregorian calendar up to the year 2100 without any external control intervention. It takes account of all the short and long months, of the twenty-ninth February, and of the leap years. The necessary control is performed in the movement by so-called program wheels.

The perpetual calendar can already be found astronomical clocks in Geneva at the beginning of the 17th Century.

In the Gregorian calendar the year 2100 is not a leap year. Some perpetual calendars (eg by IWC) support the consideration of this exception by a single operator intervention.

After a further definition of the perpetual calendar also moon age and moon phase are included. Also a leap year indicator is possible, indicating in which year of the 4-years cycle you are.

With the so-called "semi-perpetual" calendar (also: annual calendar) the leap year, thus the 29th February in every four years, is not included.

For portable watches, there are two systems:

  • the parallel running perpetual calendar: Here the passage of the hands a number to the other happens in two different speeds, at first slowly, then rapidly. In addition, date and day of week don't always jump exactly at the same time.
  • the jumping perpetual calendar: here the days, months and date star is switched by a rocker in one quick motion at exactly the same time.

Wristwatches with perpetual calendars were manufactured by Patek Philippe as early as 1930 in single copies. From 1941 they were produced as standard by Valjoux on the basis of a 13-ligne ebauche movement. In 1950 also Audemars Piguet brought a wristwatch with perpetual calendar to market.

See also: