CALENDARS, DEFINED
A perpetual calendar requires vastly more complex engineering — if not higher math — than a regular or an annual calendar function. In whichever type of calendar function though, what is common between them is that a gear in the watch movement revolves day and date display — needs to be adjusted five times in the course of a year to keep its day/ date display correct. This is to account for the different number of days in a month, so the date has to be advanced to 1 on months following those ending in 30. Or 28 or 29, in the case of February.
An annual calendar function does the regular calendar one better by “knowing” which months end in 30, and which end in 31. What it does not account for is February, and so an annual calendar needs to be adjusted every March 1. Also, it cannot tell the years when February throws a tantrum and takes an extra day for itself.
As is commonly known, a year with a Feb. 29 is called a leap year. What is less well known is Pope Chatrath, general manager for Patek Philippe’s business in southeast Asia, a “perpetual calendar must be smart enough to recognize if it’s a 28-day month, a 29-day month, a 30-day month or a 31-day month.”
PERPETUALLY PATEK PHILIPPE
Patek Philippe has dedicated much effort in tracking such intricacies of the calendar, merging astronomy with haute horlogerie in the process. It lists 27 references (or models, not including the variations of each) of perpetual calendar watches from 1941 to 2017, with three other models built between 1925 and 1937. Among these, the most notable, as cited by Ms. Chatrath, are the manually wound Ref. 96 of 1937, which featured a retrograde hand for the date display; the manually wound Ref. 1526 sold from 1941 until 1952, which pioneered the day and month apertures located at 12 o’clock; references 3448 and 3450 that were available from 1962 to 1985, which distinguish themselves as the first self-winding perpetual calendars for the brand; and the Ref. 3940 which replaced the 3448 and 3450. The Ref. 3940 was the first Patek Philippe perpetual calendar to use an extra thin caliber, a practice adopted by most of the subsequent models.
In 2014 Patek Philippe marked its 175th anniversary by taking the perpetual calendar complication for wristwatches further through its Ref. 5175 Grandmaster Chime. This piece, considered the brand’s most complicated wristwatch to date, adds two types of sonnerie, a minute repeater, a date repeater, an alarm, a moon phase indicator, and a second time zone to its perpetual calendar function. Because of this, it is also regarded as one of the most complicated watches in history.
Meanwhile, for 2018, Patek Philippe at Baselworld — the annual Swiss horology and jewelry expo — released the Ref. 5270 and the Ref. 5740, a Nautilus model fitted with a perpetual calendar. Clearly, its pursuit of the technology continues.
Crediting the brand’s “93-year experience at making perpetual calendars” as key to its mastery of the complication, Ms. Chatrath noted that Patek Philippe pieces with such functions would need to have their dates adjusted only by the time Jan. 1, 2100 rolls around (a centurial that isn’t a leap year, by the way) so these could determine the next sequence of leap years. Now, the Gregorian calendar is computed to lose only one day in 3,030 years. By all indications, Patek Philippe perpetual calendars are just as accurate. —