The In-Line Perpetual Calendar is a true Patek Philippe connoisseur piece

The oversized date, the off-centre year, the multiple sub-dials indicating a variety of information or at least a couple of apertures… Differences in application to this thing of beauty called the perpetual calendar vary among brands.

The perpetual calendar requires all the know-how a watchmaker can muster to perfect it. After all, it is poetically named as such because the encased technical mastery lulls the wearer into a sense of calm, belying the underlying dedication from watchmakers who enable the perpetual calendar to attain a level of accuracy that stays consistent for the rest of the century. Too often, however, the need to condense all the rich details pertaining to time, dates, weeks, years and leap years, as well as all the minute components that enable the watch to function exactly as intended, culminates in convoluted aesthetics.

And so, this is precisely why our curiosity is piqued by the Patek Philippe Ref. 5236P-001 In-line Perpetual Calendar. What appears rather visually simple on the surface has placed the manufacture who created its first perpetual calendar wristwatch back in 1925 under such demand to unearth ingenious solutions to express the celebrated complication in a seldom explored interpretation, allowing the day of the week, the date and the month to be put in such proximity to each other. 

“The concept of this in-line perpetual calendar dates far back in time,” Philip Barat, the manufacture’s head of watch development, says, referring to the 1972 pocket watch, Ref. 725/4 Lépine, featuring an in-line aperture now residing in the brand’s Geneva museum. 

While the inspiration is established, the real challenge merely begins and despite the palpable similarity between the new wristwatch and the original pocket watch, the copy-and-paste approach doesn’t translate into reality. The hurdle? 

“We can’t build on the idea of the pocket watch with a single large-sized date disc because in a wristwatch, the display would simply have been too small,” explains Barat. Undeterred, however, about five or six years ago, CEO Thierry Stern proposed the product development team to confront the challenge. His justification being that the market would be receptive to perpetual calendars dissimilar to existing types. 

“We went to work and muse whether we could display the date with two discs to make the perpetual calendar more legible, with a unit disc and a tens disc. So, we developed the concept of double ball bearings and applied for a patent on this idea. With them, we could place four discs in one plane,” offers Barat, describing the coplanar arrangement anchoring this particular watch. 

“But we still needed to find solutions to keep the perpetual calendar as thin as possible. Dependability, slenderness and aesthetics are key.” 

In contemporary resources and tools, they found their answers. According to the brand, the perpetual calendar mechanism (including a 12-month cam and a satellite cam for the month of February) is designed as a separate module with its own plate. This is a preferred solution for this movement, thanks to which the overall height of the calibre is smaller than with a partially integrated mechanism. The connection of the calendar with the basic movement is established with an intermediate wheel that engages with the hour-wheel pipe (a pinion that controls the minute hand). This second minute wheel is suspended between two jewels and meshes with a 24-hour wheel, also between jewels, which guarantees optimised energy efficiency. 

“There is also an intermediate unit wheel with two superposed wheel plates pressed apart by a screen. This way, it works like a surprise piece of a minute repeater that suppresses the minute strike at the top of a quarter hour. Here, it ensures that in the event of a jolt, or the quick adjustment of the date, the disc doesn’t jump by a tooth in either direction. It is a type of blocking mechanism,” elaborates Barat, adding that they assembled a working dial to verify the concept works perfectly beyond virtual simulation. 

To put things into perspective, this coplanar display alone calls for an additional 118 components vis-a-vis a conventional perpetual calendar display. The aforementioned working dial is one of 80 different tools required for the assembly process, while for the production of the parts, Patek Philippe crafted 600 different bearings, milling cutters, chamfering tools and chamfering keys. 

A technical triumph on its own, this watch is crowned by three separate patents: the ball-bearing display mechanism, the shock absorber mechanism and/or anti-double-jump feature for the movement, and the transition of the date from 31 to 1 handled by a 31-point star omitting two teeth. The calibre 31-260 PS QL is an automatic movement comprising 503 parts in total. It is fitted with a reduction wheel that uncouples the automatic winder as soon as the movement is being manually wound. The torque of the spring barrel has been increased by 20% to deliver consistent energy, while the frequency is elevated from 3.2 to 4Hz. Storing at least 38 hours of power reserve, the movement counts a unidirectional platinum micro-rotor and impresses with a height of 5.8mm altogether. 

To complement the unique display, two tiny indicators flanking either side at 4 and 8 o’clock respectively indicate the leap year cycle and day or night. While the perpetual calendar’s essence lies in numbers, its emotional appeal is epitomised by the beautiful moon-phase indicator. On this watch, the moon shares the same space with a small second display, freeing the rest of the dial surface to accentuate the splendid finishing accomplished with satin-brushed blue lacquer in black gradation. The hands are made of 18k white gold, as are the applied hour markers. 

To facilitate the adjustment of the functions, three correctors – for the day, the date, and the month – are recessed in the case flank between 9 and 2 o’clock, in the same order as the respective displays. The moon-phase corrector is positioned at 8 o’clock. The adjustment can be performed using a provided stylus in ebony and 18k white gold. 

Made of 41.3mm-diameter 950 platinum, the case is exceptionally slim for a perpetual calendar. At 11.07mm in height, the case is further encrusted with a diamond at 6 o’clock. 

(All images: Patek Philippe)

This story was first published on Prestige Malaysia.