In 2021, Patek Philippe expanded its extensive collection of calendar watches by introducing a new perpetual calendar that displays the day, date, and month side by side in a large window at 12 o'clock. How did Patek Philippe's engineers create this movement?
Text by By Pierre Maillard
Article published on June 2021, 10
A new perpetual calendar inspired by the company's archives
Designing a perpetual calendar is one of the highest ideals in watchmaking. As the name suggests, the goal is to create a mechanical representation of a great celestial clock, one that never interrupts the flow of time. What greater accomplishment could a watchmaker have than creating a mechanism that displays the hours of the day, week, month, and year with unerring precision? As the French philosopher and deist Voltaire said, was God himself the "great clockmaker"?
Today, most of us live our lives according to the division of the year established by the Gregorian calendar, which was introduced by Pope Gregory XIII in 1582 to more closely resemble the sundial. Unwilling to accept the Pope's proposal, Protestant countries, known to have "fallen out of love with the sun," opted for the Julian calendar, which was cumulatively about 11 days behind the sundial (roughly one day per century).
So, in 1582, countries that adopted the Gregorian calendar added October 15th immediately after October 4th to correct for the delay. Since then, the Gregorian calendar has become more accurate than the sun, but to maintain accuracy, it requires adding a day to February every four years and making an exception for a leap year at the end of the century (and again in the 400th year). This presented a challenge to watchmakers: to incorporate astronomical calculations into their mechanical timepieces.
Patek Philippe excelled in the perpetual calendar technology, perfected at the end of the 18th century. This is eloquently demonstrated by the numerous pocket watches produced by Patek Philippe. In 1925, Patek Philippe also completed the world's first wristwatch with a perpetual calendar.
A surprisingly simple appearance and a terrifyingly complex mechanism
Clarity and legibility of the time and calendar displays are essential elements of a perpetual calendar, and these elements are often accompanied by a moon phase to complete the whole. Over the years, Patek Philippe has offered various displays, such as hands on a subdial (as in models with the caliber 240 Q) or two apertures for the day and month.
Another display method was found only in a few pocket watches and never before seen on a wristwatch: the 1972 pocket watch Inv. P-72, which displayed the day, date, and month in a single line at 12 o'clock. This watch, housed at the Patek Philippe Museum in Geneva, caught the eye of Patek Philippe's engineers and served as inspiration for the new perpetual calendar, Ref. 5236.
From a horological perspective, this single-row layout is the geometric and graphic expression of the essence of a good perpetual calendar, displaying uncluttered information that can be read at a glance.However, engineers knew that incorporating such a calendar display into a wristwatch would pose many technical challenges.
