The perpetual calendar watch has a mechanical
memory programmed for times to come. It will
show the correct date for a whole century without
any manual correction.
While the astronomical year, determined by the revolution of the Earth about the Sun, is 365.2422 days long, it is essential that the civil year should comprise a whole number of days. This is the reason for leap years, instituted by Julius Caesar in 46 BC. In this system, the month of February is one day longer than usual every fourth year.
Taking this into account when designing a date display demands top-class watchmaking skill. While annual calendar watches take account of variations in length between the months, only the perpetual calendar watch is capable of displaying the day, the month and the date without any manual correction, even in leap years. As a finishing touch, this exceptional timepiece also displays the phases of the moon.
Invented in 1853, the movement capable of identifying leap years is a genuine mechanical memory. A small satellite gear wheel connected with the month mechanism completes one revolution every four years. In the fourth year, this mechanism displays 29th February before changing directly to 1st March. Like the Moon orbiting the Earth, this satellite wheel turns about its own axis, in contact with a pivoting wheel.
This complication, which unites utility with technical prowess, is one of the masterpieces of the watchmaker’s art. Fired with the ambition to do more than simply follow in the footsteps of their predecessors, Blancpain’s watchmakers have succeeded in creating the world’s slimmest perpetual-calendar watch, presented in 2000, and in facilitating regulation by an arrangement of correctors under the horns, patented by the Le Brassus Manufacture.
The perpetual-calendar watch is perfectly adapted to the Julian calendar. However, since 1582, our societies have gradually adopted the Gregorian calendar, in order to correct the small time-lag of 0.0078 days per year that remained despite the leap-year system introduced by Julius Caesar at the instigation of Sosigenes of Alexandria. In the Gregorian calendar, named after Pope Gregory XIII, one leap year is suppressed every one hundred years, except when the secular year is divisible by 400. Thus, 2000 was a leap year and 2400 will be another, but 2100, 2200 and 2300 will not be. This means that the proud possessor of a Blancpain perpetual-calendar watch will nevertheless be obliged to correct their date display three times in the course of the next five centuries!