The perpetual calendar—or quantième perpétuel (“QP”) for the Francophones among us—has been kicking around the horological world for nearly three centuries. Thomas Mudge, an English watchmaker, was the first to build a pocket watch that displayed the day, date, month, phase of the moon, and accounted for Februaries of different lengths by tracking leap years. This sophisticated pocket watch, No. 525, was completed in 1762, over a decade before the American Revolutionary War. Today, QPs are more common amongst high-end watchmakers, but still stunning in their mechanical complexity. Models from the so-called “Holy Trinity” of brands—Patek Philippe, Audemars Piguet, and Vacheron Constantin—are particularly sought after. A.P.’s history of QP manufacturing actually dates to the company’s founding, when Jules Louis Audemars completed a school pocket watch that combined a perpetual calendar with a quarter repeater as well as a deadbeat seconds mechanism. In 1955, the maison released the world’s first perpetual calendar wristwatch with a leap year indicator; in 1978,..
