At the online edition of Watches and Wonders in 2021, Patek Philippe released a revolutionary new reference, the 5236P-001. Part of the Calatrava line, this vintage-inspired model in platinum included a perpetual calendar mechanism with automatic winding — certainly not a novel design for Patek Philippe. However, the 5236P-001 marked the first instance of an in-line perpetual calendar display being used in a Patek Philippe wristwatch. But what exactly is an in-line, or “American,” perpetual calendar display, and why is it so novel?
Patek Philippe In-Line Perpetual Calendar Ref.5236P-001 - IN THE SHOP
True to its descriptor, an in-line perpetual calendar is one in which the day, date, and month are displayed in a single row of apertures. The “American” nomenclature derives from the fact that such displays were historically arranged in the American fashion — month followed by date — due to their sale in the American market. (If you’re an American and you’ve ever been taken aback by a date that looks like this — 31/05/25 — it’s because most of the rest of the world displays the date first, then the month.) Patek made a relatively small number of in-line QP pocket watches during the mid-20th century scattered across a handful of references, but miniaturizing the display for a wristwatch proved to be an incredibly difficult proposition that would take decades. (More on that later).
The Pocket Watches
In 1940, Patek Philippe introduced a pocket watch that would have an outsize impact upon the design of some of its most significant complicated wristwatches: The Ref. 725, produced in yellow gold, pink gold, and platinum in four sub-references (/1, /2, /3, /4), was primarily configured with four subdials displaying the month; the date; the moon phase; and the day of the week at the different cardinal locations. (Different sub-references arrange the indications in different positions.)
Utilizing the hand-wound Calibre 17-170 movement from Victorin Piguet & Cie adjusted to eight positions, it features instantaneous calendar changes and excellent finishing. As respected Patek Philippe expert John Reardon has noted, the influence of the Ref. 725 in the aforementioned configuration is visible in the design of the famed 1518, 2499, 3970, 5970, and 5270 perpetual calendar chronograph wristwatches that followed it chronologically.
Patek Philippe 'American' digital perpetual calendar in yellow gold Ref. 725/4 - (Image by Antiquorum)
Certain Ref. 725 examples feature a different display type, however: Rather than the splayed subdials of the earlier series, they feature the in-line “American” display with a moonphase subdial above 6 o’clock. Considering that only roughly 100 examples of all Ref. 725 designations were produced between roughly 1940 and 1980, the “American” versions are extremely scarce, with only a handful of examples ever having cropped up at auction.
Interestingly, certain examples feature movements that were cased years (or decades) after production or watches that were cased but only sold years (or decades) later: One Ref. 725/4 sold at Antiquorum was produced in 1956 and sold only in 1981; another Ref. 725/2 currently being offered by The Keystone was produced in 1951 but only sold in 1957. It would seem that perhaps these elegant, complicated timepieces, produced during an era when the pocket watch had already been eclipsed by the wristwatch, had some trouble finding an audience.
Patek Philippe yellow gold perpetual calendar pocket watch Ref. 725/2 - (Image by The Keystone)
Another notable example of the in-line perpetual calendar display used in pocket watch form is the Reference 699/2, a QP with minute repeater produced between 1939 and roughly 1964 and of which only a handful examples are known to collectors. Two different configurations have appeared at auction: One example sold at Phillips in 2016 looks not dissimilar to the Ref. 725 with in-line display and moon phase indicator above 6 o’clock — however, a trigger on the right-hand case flank indicates the presence of a minute repeater mechanism. This particular example is striking for its construction history: Its Calibre 17’’’ movement was finished in 1930, while the watch was cased in 1957 and sold in 1960. A second configuration, sold at Christies in 2020, replaces the moon phase display with a power reserve indicator. This piece’s history stretches back even further in time: An Extract from the Archives confirms production of the movement in 1921 and sale of the watch in 1960.
Patek Philippe 'American Calendar' Ref. 844 - (Image by Sotheby's)
A third example of Patek’s in-line perpetual calendar pocket production is the Reference 844, a white gold minute-repeating QP introduced in 1965. Measuring 51mm in diameter and housed in a case produced by Antoine Gerlach with a stepped bezel and contrasting polished and satin-finished surfaces, it features an in-line calendar display, a moon phase display above 6 o’clock, and applied white gold indices and ‘dauphine’ hands. An example sold by Phillips in 2023 previously belonging to none other than Jean-Claude Biver was produced in 1972 and sold in 1989. Its movement, the Calibre 17’’’, is the same as that which powers the Ref. 699/2, and it is one of just two examples known in white gold. Another example in yellow gold sold by Sotheby’s features a movement produced in 1930 that was sold only in 1967.
Clearly, Patek Philippe was an early innovator in the realm of in-line QP displays, having produced its first such movements over a century ago and slowly innovated and iterated upon the design during the ensuing decades. It would seem that given the low production numbers and high cost associated with designing and producing such complicated pieces that only the maison’s very best clients would be offered such watches for purchase.
The Wristwatches
Patek Philippe In-Line Perpetual Calendar Ref.5236P-001 - IN THE SHOP
This brings us back to 2021 and the debut of the 5236P-001. As explained to Wei Koh of Revolution by Patek Philippe’s head of watch development, Philippe Barat, miniaturizing the in-line display for a wristwatch was no easy feat: Within a larger pocket watch, using a single disc to display both single- as well as double-digit dates isn’t problematic — employing this system within the confines of a 41.3mm wristwatch, however, would’ve resulted in typeface that was too small to be easily legible.
The solution was to use two discs for the date: One showing the tens digits, and the other showing the ones digits. The four total discs (one for the day of the week, two for the date, and one for the month) are then mounted on a single plane on ball bearings to prevent them from touching one another. Two additional apertures, one for the leap year and the other indicating day/night, flank the moon phase display to the right and left, respectively.
Take note that this in-line display is not, like the aforementioned pocket watches, arranged in the American fashion, but in the European mode in which the date precedes the month. (And, in this case, the day of the week precedes both.) Given a blue gradient dial with vertical brushing; an outer printed ‘railroad’ minute track in white against a blue background; a radially finished moon phase display with white printing; and a beautiful set of applied, faceted indices and a matching ‘pencil’ handset, the Ref. 5236P-001 is a stunning, highly contemporary mix of the maison’s midcentury, in-line QP pocket watches with an added sprinkling of aesthetic influence from wristwatch references such as the 3448 thrown in for good measure. Its movement, the freshly designed Calibre 31-260 PS QL, features 503 components, automatic winding via an off-center platinum micro-rotor, and a power reserve of 38-48 hours.
Patek Philippe - (Image by Patek Philippe)
Joined in 2024 by an opaline rose-gold dial version, the Ref. 5236P-010, the in-line perpetual calendar is slowly growing into a full sub-collection within the larger world of Patek Philippe wristwatch QPs. Now that the brand has developed a modern movement that successfully adapts this sophisticated display type for the wrist, can we perhaps expect to see other references crop up in the future — perhaps in other collections — that will take advantage of its elegant-yet-idiosyncratic mechanics? There’s certainly reason to believe so. There are all manner of perpetual calendars within the Patek Philippe catalog, meaning that there’s clearly an appetite within the collector community for this compelling (yet expensive) complication. Doing what it does best, Patek developed the in-line QP over the course of a century until such time as it could be appropriately and beautifully utilized on the wrist.
Who wouldn’t want to experience such a luxurious way to discern the time?
