Patek Philippe produced the first Swiss wristwatch with a perpetual calendar in 1925.
A perpetual calendar is a highly complex complication that displays the date, day, month and often moon phase while accounting for months of different lengths and leap years. Unlike a simple calendar, it usually needs correction only after a calendar-century year that is not divisible by 400.
Patek Philippe had already established a reputation for complicated pocket watches before applying this mechanism to a wristwatch. The 1925 achievement helped demonstrate that wristwatches could house sophisticated calendar mechanisms, not merely timekeeping functions.
This milestone is sometimes confused with Patek Philippe’s first perpetual-calendar chronograph wristwatch, a later development. It is also distinct from the company’s famous 1941 Ref. 1518, noted for combining a perpetual calendar with a chronograph in serial production.