Created somewhere between the mid to late 1920s, many understand the primacy of the perpetual calendar as a milestone complication denoting watchmaking prowess but fewer understand the complexities and just how miraculous the operation of a perpetual calendar really is.
With smartphones, displaying leap year, equation of time, complete dates are as simple as unlocking the phone and running the calendar app. Even as the smartphone displays the multitude of data points in a graphical interface, a programmer has worked beyond the scenes to collate and calculate using a series of mathematical tables, the complete timeline for the next 1000 years. In that perspective, a silicon microchip a sliver the thickness of your fingernail runs and computes all that data right down to the phases of the moon. Now, in this context, consider the mechanical perpetual calendar, bereft of microchips and text-based computer programming languages, a watchmaker is left with his wits and the determination to shape a series of gears and cams into a workable mechanical calendar, a veritable wristworn computer, 100 years before the birth of the smartwatch.
History of the Perpetual Calendar
Taking the form of a ladies’ pendant watch in 1898, Patek Philippe’s 97975 calibre was a perpetual calendar with an additional moonphase complication. While it was groundbreaking, its initial positioning as a ladies’ watch didn’t allow the revolutionary calibre to enter patriarchal consciousness until 1925, when the Geneva manufacture began production of wristworn perpetual calendars.
Then in 1929, Breguet themselves manufactured a Ref. no. 2516 which was sold to Monsieur Jean Dollfus in 1934 for the princely sum of 11,000 Francs. Given the rarity of vintage Breguet watches beyond the pilot chronograph Type XX collection, Christie’s last auction in 2011, Lot 427 was a veritable treasure trove with once such gem. A Perpetual Calendar Breguet no. 2516 with circular nickel-finished lever movement, bimetallic compensation balance and Breguet balance spring. It’s tonneau shape watch with silvered matte dial was 26mm wide and 39 mm long, realising a price of US$475,618 from an estimate of US$340,909.
By 1937, the Grande Maison Jaeger-LeCoultre had a turn, celebrating the merger of Edmond Jaeger and LeCoultre with their own groundbreaking perpetual calendar. While the Jaeger-LeCoultre was kept hidden and signed only on the in-house calibre, the words “Perpetual Calendar” ran proudly on the dial of the rectangular timepiece, demarking it for anglo-saxon markets.
Interestingly, though perpetual calendars solved the conundrum of making manual adjustments for leap years; only the original perpetual calendar pocket watches displayed leap years, the wristworn versions did not have leap indications until 1955 when Audemars Piguet produced a collection of perpetual calendars with leap year indication.
Operation of the Perpetual Calendar
While the underlying operating principles of a perpetual calendar might be similar, each brand espouses different architecture. While “component count” isn’t exactly a useful barometer to determine how complex a mechanism is (easily inflated with unnecessary bridges, screws and jewels), for the perpetual calendar, the nature of calculating number of months, number of days in each month, adjusted for leap year, while keeping track of the year itself, requires over 100 additional components. Design of one takes years while assembly and construction of one takes months.
Consider this, modern computer aided design implies that while the planning and prototyping might be simplified, production is still overwhelming challenging- anything produced in strict direction to computer designed specifics will result in gears, wheels and cams which “operate in theory” but are too tight in practice, the lack of “give” means that the watchmaker then has to individually shape each component to the point where the tolerances between each part and component is precision yet still given enough space or “give” to move. Add to the fact that a modern perpetual calendar is usually of the “instant jump” variety, the art of constructing a whole perpetual calendar just becomes all the more daunting.
As the name suggests, a “perpetual” calendar infers that the date calculations will run perfectly without external intervention even in the leap years thanks to programmed mechanical memory of 4 years spanning 1461 days. Typically, the date wheel will have 12 sectors corresponding to each of the 12 months in a year. Each sector will then be cut with teeth to correspond to the appropriate length of the month – some months have 30 days, others have 31 and one sector for the oddity that is February will have an additional cam or component under it to facilitate the addition or subtraction of a day depending on the leap year.
For the more traditional 30 or 31 day months, their gear teeth accounts for the differences of a single day with either a shallower notch on one of the teeth for the former. When the perpetual lever detects a shallower or regular notch relative to its position, the lever than determines the appropriate number of steps (aka days) it should advance on the day and date wheels at the end of the month.
For February, the extra component beneath calculates the leap year. Containing four sectors, the fourth notch accounts for the 4th year representing the leap year. Over the course of time, the perpetual lever will “detect” your three standard years and then engage February 28th while on the fourth, the lever detects a differentiated marker and then engages a different set to trigger February 29th.
To wit, it’s possible to infer that when conceived in the early 19th century, it was ingenious and downright magical. Today, our modern computers may render the task a smidgen simpler but nevertheless, the perpetual calendar complication is an endeavour that only the few heritage brands like Jaeger-LeCoultre should undertake.
The fictional magic of Doctor Strange notwithstanding, the perpetual calendars like Jaeger-LeCoultre’s Master Ultra Thin Perpetual Calendar have a real genius and nigh miraculous quality behind them. Thanks to the advent of material sciences and technological advances, a modern tourbillon might convey the spirit and majesty of the tourbillon’s “gravity-compensating” principles but its position as a complication is one of artistry and watchmaking showmanship. For a complication like the Perpetual Calendar, it’s function is still very much a practical one and a rebellion of brass and steel in the face of the advancing microchip.