Perpetual Calendar
A perpetual calendar (quantième perpétuel) accounts for months of 28, 30 and 31 days as well as the four-year leap cycle. Because the Gregorian calendar drops a leap day in centennial years not divisible by 400, every standard perpetual will require correction on 1 March 2100.
Origin
Thomas Mudge built the first known perpetual-calendar pocket watch around 1762. The first perpetual-calendar wristwatch is generally attributed to Patek Philippe, reference 97 975, completed in 1925 on a women's pendant-watch movement from 1898.
Construction
A perpetual calendar relies on a 48-month cam (the 'grand levier') that mechanically encodes month length and leap year. Higher-end calibres add a moonphase, retrograde date, or an instantaneous jump for all indications at midnight.
Reference movements
Patek Philippe calibre 240 Q, Audemars Piguet calibre 5134, Vacheron Constantin calibre 1120 QP, IWC calibre 52610 (Kurt Klaus design, 1985 - adjustable from the crown only) and A. Lange & Söhne L021.3.
Key facts
- ▸First wristwatch perpetual: Patek Philippe ref. 97 975 (1925)
- ▸Next required correction: 1 March 2100
- ▸Distinct from 'annual calendar' which needs adjustment each 1 March