Seeing The Centuries: Different Displays For The Perpetual Calendar
The complexity of the perpetual calendar means that when it comes to variety in their displays, the sky’s the limit.
The perpetual calendar exists for one fundamental reason. The amount of time that it takes for the Earth to go once around the Sun is not a whole number of days – instead, it takes on average, 365.2422 days. This means that if you have a calendar based on a 365 day year, you will be off by a day in about four years but you can make up for this by adding a day once every four years. The Julian calendar, which preceded the current Gregorian calendar, added an extra day once every four years but since the year is slightly less than 365.25 days long, an error gradually accumulated of about three days every four hundred years. By the mid-16th century the Julian calendar had drifted out of alignment with the seasons by about ten days – three days every four hundred years eventually adds up. To correct this error and keep the calendar aligned with the seasons and the equinoxes (and to keep things like the date of Easter consistent) Pope Gregory XIII decreed in 1582 that moving ahead, the calendar would be based on a year of 365.2425 days. In addition to a Leap Year every four years, we would skip the Leap Year every 100 years, but then add it back in every 400 years. The US Naval Observatory puts it succinctly:
“Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.”
Watchmakers and clockmakers have a lot of options when it comes to implementing a perpetual calendar and over the centuries there have been a number of different designs. The first mechanical timekeeper to mechanically add the 29th of February that I have been able to find, is a mechanical celestial sphere made by the mathematician, horologist, and polymath Jöst Bürgi, perhaps the greatest horologist of his time (he is also credited with co-inventing logarithms, along with John Napier). His celestial sphere, was completed in 1586, just four years after the introduction of the Gregorian calendar.
The first watch that we know of which had a perpetual calendar came along around 1762 and it was made by Thomas Mudge. The display shows the date on an outer ring with a silver indicator at 12:00, and there is a month indicator, with a Leap Year window for the month of February, as well as a moonphase indicator and display for the day of the week. In terms of information displayed, this is more or less a summary of what you might call the completist approach to the perpetual calendar: Day, date, month, Leap Year, and phase of the Moon.
This particular watch was sold at Sotheby’s 2016 “Celebration Of The English Watch” sale – it was bought, appropriately enough, by Patek Philippe and is now in the Patek Museum in Geneva. It is from the collection of none other than the late David S. Landes, a Harvard professor of economics and history whose name we all should know – he is the author of Revolution In Time: Clocks And The Making Of The Modern World, which is essential reading for anyone interested in horology.
Another notable example of the perpetual calendar display comes of course from none other than Breguet, whose no. 160, the famous “Marie Antoinette” grand complication, which also included (among other things) a minute repeater, independent seconds, and Equation of Time. Interestingly enough, the watch uses a cylinder escapement – you might have expected it to have a tourbillon with detent or lever escapement, perhaps, but it’s possible such an addition would have taken up too much room and Breguet in any case is famous for the durability and accuracy of his cylinder escapements.
You might think at first that the date is shown on the month wheel at the lower left, but in fact, that wheel (which has the Equation of Time cam on top of it) is part of the perpetual calendar mechanism which shows the date via a hand at 2:00 on the dial. I have been unable to find out why the date indication begins at 0 – I thought at first it might have something to do with the Republican calendar but the names on the month wheel are the traditional calendar month names. Something to ask Breguet. The watch shown is not the original no. 160, by the way – it is no. 1160, a recreation made from Breguet’s own original plans by Breguet, and completed in 2008. The original is part of the Salomons Breguet collection housed in the L. A. Meyer Museum Of Islamic Art, in Jerusalem.
Perpetual calendars in complicated pocket watches generally followed the format seen in watches like this Audemars Piguet grand complication, perpetual calendar, minute repeater, and chronograph pocket watch, completed in 1908 and sold at Christie’s in 2018.
This particular watch is 54mm in diameter – about what you would expect for a pocket Grand Comp from the era – and displays all calendar information in subdials. The size of the watch means that including the date, day of the week, small seconds, moonphase, month, and leap year indications on the dial presents no problem in terms of available real estate, although you do kind of see what George Daniels meant when he said that designing a complicated watch means running the risk of having something that looks “like a gas meter.”
From The Pocket To The Wrist
Shrinking the displays down to wristwatch size just makes the problem worse, although the first generation of wristwatch perpetual calendars gave it a shot. Patek Philippe’s first wristwatch perpetual calendar, no. 97975, from 1925, took this approach, albeit the watch used a movement made in 1898 and which was originally meant for a ladies’ pendant watch.
This was more or less business as usual up to this point. However, quite quickly, people’s notions of design in perpetual calendars was shifting to a preference for something less cluttered, more legible, and more in tune with the overall design trends of the time.
This is a Patek Philippe perpetual calendar minute repeater from just five years later – 1930 – and it just goes to show you how fast things were moving in perpetual calendar design. This particular model, ref. 844, was sold by Sotheby’s in May of last year and while it shows almost all the information of its predecessor (except for an indication of the Leap Year) it is so much cleaner, legible, and uncluttered that it is hard to believe the two watches have the same complication (ref. 844 has a repeater while ref. 97975 doesn’t but of course, the repeater is not a visual complication). This watch is by the way, also an example of a so-called “American” calendar display, with a month, date, and day of the week format.
The Icon: Patek’s Ref. 1526
By the time Patek Philippe began making series produced perpetual calendars, the trend towards cleaner and less cluttered perpetual calendar displays was firmly established in the company’s design language.
And here is the first series produced perpetual calendar wristwatch, the ref. 1526, which Patek Philippe began producing in 1941. It’s hard to believe that this is a descendant of the ref. 97975 from just sixteen years before, but that’s how fast things were moving. It’s not quite as crisp and clean as the ref. 844 but then again, this is a wristwatch and reducing the number of windows to two, probably saved some space in terms of movement dimensions (the 1526 is a 34mm watch, vs. 51mm for the ref. 844 pocket watch). Day, month, date, small seconds and the moonphase are all present – once again, the only thing missing is a leap year display – and as a model of clarity and purity of design, the 1526 has continued to set the standard for perpetual calendar wristwatches right down to the present day.
Basically, without exception, and with of course a number of variations in details, this is the format that Patek Philippe stayed with right up until the introduction of the ref. 3940, in 1985. This reference was a little bit of a step away from the almost radical clarity of the 1526 and its descendants – all the information was shown in subdials, with the Leap Year indication sharing a subdial with the month indicator. As you can see in one of Tim’s video reviews, though, you would hardly call this a cluttered watch.
Patek Philippe is strongly identified with perpetual calendars for a reason – among their firsts is the production of the first series produced retrograde display perpetual calendar, the ref. 5040. (Patek also produced the first retrograde perpetual calendar of any kind – that was the ref. 96, made in 1937. In 1993, the company launched the first series produced retrograde perpetual calendar: the reference 5050.
As you can see, this is another example of a watch with a complete perpetual calendar display – the Leap Year indication is just above “Patek Philippe” on the dial and the retrograde date gives you something a little more dynamic to look forward to at the end of the month than the usual perpetual calendar display – it makes for a slightly busier dial than the classic 1526 layout and its relations, but it also addresses one of the disadvantages of the perpetual calendar in terms of entertainment value, relative to, say, a rattrapante chronograph.
One of my favorite examples of a variation on the perpetual calendar is from De Bethune – the DB25 perpetual calendar.
On the face of it this is another variation on the basic layout of the classic perpetual calendar – two windows for the day of the week and the month, with a subdial for the date, and a moonphase display. What sets this watch apart, of course, is the spherical moonphase display, which is a beautiful variation on perpetual calendar business as usual, and which contributes significantly to the strong identity of the watch overall. Despite the fact that there is nothing about the DB25 Perpetual which is a radical departure from traditional perpetual calendar design, it is a great example of just how creative you can get working within the context of imaginative variations on traditional themes.
Thinking Outside The Box
Once you depart from the more or less classic design language established by Patek in 1941, things start to diversify with amazing speed. One of the most interesting variations on the traditional perpetual calendar is the A. Lange & Söhne Lange 1 Perpetual Calendar Tourbillon.
The full range of perpetual calendar indications is on the dial and of course, the signature big date display is now a perpetual date display. There’s an indication for the day of the week, and a small Leap Year window at 6:00; the power reserve is the small rotating triangle at 6:00 in the subdial. The month is shown on a rotating disk on the periphery of the dial, with a pointer just below the Leap Year window. This is as we’ll see something of a theme in watches that depart from the classic perpetual calendar configuration – design and engineering innovation necessarily go hand in hand, as where the various indications are and how they’re implemented, is a direct consequence of the design of the movement.
Now there is of course, no reason that clarity and economy of means should be the only guiding philosophy behind perpetual calendar design. I mean, sometimes you just lean into the maximalism, and lean hard.
This Roger Dubuis from the early 2000s is admittedly a bit of a cheat in a discussion of variety in perpetual calendar displays as it is a perpetual calendar plus chronograph, but I would just plea that you could take away everything to do with chronographs from the design and still have one of the most exuberantly, floridly baroque perpetuals ever made. Just look at it – the typefaces for the date and day are elongated to within an inch of their lives, you’ve got more hands than a Las Vegas poker tournament and that outer week scale means you will never have to worry if you’re in the 35th or 36th week of the year again.
This is a watch from a time when the question in watch design wasn’t “why” it was “WHY NOT” and I love how true it is to its own identity. You almost expect to see it belting, “I Gotta Be Me” on karaoke night.
Speaking of asking, “WHY NOT” here is another one of my favorite unconventional perpetual calendars: The Cartier Astrocalendaire, from 2014. This particular perpetual calendar was developed by Carole Forstier-Kasapi, during her time as head of movement development at Cartier and it is certainly unlike anything before or since.
This is a perpetual calendar with the indications arranged in a sort of amphitheater, with a tourbillon at the center (the Leap Year indication is on the back). The day, date, and month are read off from the moving open rectangles. This is despite its highly complex appearance a very user friendly perpetual – it dispenses entirely with the usual system of cams and levers and instead relies on a system of gears with retractable teeth to keep the calendar up to date. It may or may not fit your preconceptions of what a perpetual calendar should look like, but like the Roger Dubuis, you can for sure say, at the very least, you’d never mistake it for a 1526. I thought it was ingenious in 2014 and I still think so.
More recently, MB&F launched the Legacy Machine LM EVO perpetual calendar. This particular take on the perpetual calendar began with a design brief which stipulated that the perpetual calendar mechanism should be elevated above the plane of the dial (along with the signature elevated balance, under its double-arched bridge). The challenge was that a traditional perpetual calendar mechanism is controlled by a complex, multi-armed lever which sits more or less in the center of the movement, under the dial. To get around this, watchmaker Stephen McDonnell had to redesign the entire perpetual calendar mechanism.
Like the Cartier Astrocalendrier, this is an example of the integration of design and watchmaking to a single overall goal, which is to produce an experientially, technically, and aesthetically integrated version of one of watchmaking’s most traditional complications.
Now, so far we have seen some examples of the old-school Baroque approach, the mid-20th century clean and uncluttered approach, and a couple of examples of Neo-Baroque/Maximalist perpetual calendar design. However, creative minds have also turned themselves to exploring how you can do more with less – I think the most notable example is and has for quite some time, been Moser, who launched their Perpetual 1 in 2005. The most recent version of their perpetual calendar, in their signature Streamliner case, is as austerely beautiful as a perpetual calendar gets.
This is the perpetual calendar carefully reduced to an absolute minimum. The only indications other than the hours, minutes and seconds, are the date window set opposite the crown, the power reserve indicator symmetrically opposed to it at about 10:00, and the month indicator. The latter is on the same axis as the hour and minute hands and it shows the month by pointing to the position on the dial which, if the dial had 12 markers for the hours, would correspond to the month. This is the cleanest version of Moser’s perpetual calendar yet (the Leap Year indicator is on the back) with not even the Moser logo on the dial.
Finally, there’s a watch with a different take on minimalism – one which began with the question, “How few parts can you use to make a perpetual calendar?” That question was answered by Dr. Ludwig Oechslin, the mathematician, watchmaker, and engineer behind some of Ulysse Nardin’s most sophisticated complications, at his own watch brand, Ochs Und Junior.
Now this looks confusing as hell at first but once you understand the set-up, the date and other indications are surprisingly easy to read. The four dots on the inner rotating disk, indicated the month; the outermost dot points to the position on the dial which, if the dial were marked off in twelfths, would correspond to the month. When the black dot is the outermost dot, it’s a leap year. The date is shown by the position of a black dot in one of the 31 apertures around the outer dial and the black indexes divide those dots into groups of five (in the above image, it’s the 9th.) The small upper disk is the power reserve indicator and the lower is a running small seconds indicator.
This perpetual calendar overall requires only nine additional parts and the radical reduction in parts count – which also means better reliability – is thanks to the fact that the mobile elements of the perpetual calendar are used as indicators themselves. Conventional perpetual calendars may have a hundred or more additional components, depending on the design.
The last 20 years have seen an incredible diversification of the design language of perpetual calendars. The pendulum nowadays has swung somewhat back to a preference for more traditional, conventional designs but fans of creative innovation in watchmaking still have an impressive range of choices – this small survey of the field is anything but comprehensive. With this year’s major product introductions still to come, we’re looking forward to seeing who might be the next to bring best of class traditional perpetual calendars to the party – and who might, as MB&F, Cartier, Ochs Und Junior, and others have done in the past, show us something we’ve never seen before.