Crowning Achievement: Audemars Piguet Launches Three New Perpetual Calendars With Groundbreaking Caliber 7138
The new movement is the first perpetual calendar in which all indications can be set individually from the crown, backwards or forwards.
Watchmaking is sometimes all about solving problems that don’t really exist, or at least, solving problems so minor that the amount of ingenuity expended on solving them would seem better spent on – well, almost anything really. However, the ingenuity and persistence involved in solving such problems continue to make demands on watchmakers and fascinate watch enthusiasts.
A case in point is the perpetual calendar. A perpetual calendar watch is one programmed to switch to the first of the month at the end of 30 day and 31 day months, and even at the end of February 28th or, in the case of a Leap Year, the 29th. This requires an enormous increase in complexity and, historically, fragility in a watch, as well as an enormous increase in cost, all for the dubious advantage of not having to touch the crown five times a year, which, assuming you take a minute to adjust the date, means you have saved five minutes out of the 525,600 minutes that make up a calendar year – but if watchmaking is about anything, it’s about incremental improvement. In the spirit of celebrating ingenuity, as well as showing that there’s always room for improvement, as well as also celebrating its 150th anniversary, Audemars Piguet has just announced three new watches – two Royal Oak perpetuals and one Code 11.59 which share a new movement. This is the caliber 7138 which, I believe, is the first perpetual calendar movement in which the indications can each be adjusted individually from the crown.
I say “adjusted individually from the crown” because of course, we have had perpetual calendars which can be adjusted entirely from the crown for decades, starting with the Kurt Klaus-designed IWC perpetual calendar which was introduced in the Da Vinci Perpetual Calendar Chronograph ref. 3750 in 1985. There were no recessed correctors set into the case flank and no corrector tool to lose (albeit losing one is not the end of the world, considering the cost of a box of toothpicks) and all indications were coordinated, which means that if you reset the date, all the other indications would switch over as well so that the correct day, date, month, and four-digit year display were always synchronized.
The only downside to this invention was and is that you could only set the indications forward. This meant two less-than-user-friendly things. The first is that if you accidentally set the calendar too far forward, you couldn’t set it backwards to the correct date; your only choice was to let the watch run down and wait until the actual date caught up with the watch. The other is that if the watch hadn’t been used for some time, or hadn’t been on a winder, you were depending on how behind it was, in for quite a lot of crown turning. I speak with some feeling of this idiosyncrasy having once had to reset an IWC perpetual which was three years behind, which took three or so days of intermittent crown-turning.
Since then, several perpetual calendar mechanisms have been designed which are not only synchronized, and settable from the crown, but which can also be set forwards or backwards. Examples include Moser, the Ulysse Nardin Perpetual Ludwig (and variants), the Ochs und Junior perpetual calendar, designed by Dr. Ludwig Oechslin, and Cartier’s perpetual Astrocalendrier tourbillon, from the now largely forgotten Fine Watchmaking Collection.
The only problem with these systems was that again, depending on how far ahead or behind the watch was, you might be in for an inordinate amount of crown manipulation, since there were no correctors which would allow you to reset the indications individually.
The Traditional Perpetual Calendar And How It Works
All of the aforementioned systems work by finding alternative mechanisms for switching the date correctly – alternatives to the traditional mechanism, which can be seen very clearly in the perpetual calendar plate from an A. Lange & Söhne grand complication pocket watch originally completed in 1902 and which was restored by Lange – laboriously; the movement had been exposed to water and was badly corroded – and shown publicly for the first time in 2010.
In the above photo, the date indication is at 3:00, the moonphase at 6:00, the day of the week (with its seven pointed star; often, the number of teeth on a gear wheel is a giveaway as to its function, especially in calendar complications) and, at the top, the month indication. In the actual watch, the month subdial shows all 48 months of a full four year Leap Year cycle.
The heart of the perpetual calendar mechanism is the multi-step cam at 12:00, usually known as a program wheel. The program wheel has 48 steps of varying heights and depths, and the nose of a multi-beaked “great lever” which is responsible for switching all the other indications including the date and the day of the week, sits on or in one of the steps. The four deepest steps correspond to the 28th of February, and you’ll notice that one of them is slightly less deep than the other three – this corresponds to the 29th of February, which comes around once every four years, in a Leap Year. The depth of the steps controls how far the lever pivots at the end of every month, and the greater distance traveled, the greater the number of teeth on the date disk that get indexed by the pawl at the opposite end of the great lever. At the end of the month, the rotation of the date wheel also pushes a lever that lifts the beak of the great lever out of the step, and rotates the the 48 month program wheel one step, corresponding to the next month.
In order to make the mechanism more compact, watchmakers sometimes us a twelve month program wheel, with a recess set into it holding a pivoting cube which rotates a quarter turn per year.
The mechanism is beautifully clever and for all the complexity of its operation, relatively simple. However, setting the perpetual calendar indications requires the owner to use a set of correctors set into the case flank, which is not a major drawback – but being able to adjust all indications from the crown without having to resort to fiddly little tools is an attractive possibility; hence the innovations going on since 1985, to make the whole thing a little more user friendly.
Audemars Piguet’s Perpetual Calendar Mechanism In Caliber 7138
The caliber 7138 does something that none of its predecessors have done, which is to allow you to set each of the indications individually – as you can with correctors – but all from the crown. Elements of the movement are derived from Audemars Piguet’s caliber 5133, an ultra-thin automatic perpetual first introduced in the concept watch RD #2; the movement was 32mm x 2.89mm, making it even thinner than the preceding caliber 5134, which was 29mm x 4.5mm. Both the 5134 and the 5133 were built on the caliber 2120/JLC caliber 920, and the 5133 introduced a number of interesting innovations in the pursuit of slimness in the movement construction.
The most immediately noticeable innovation is in the construction of the calendar plate. Normally (and as seen in the Lange grand comp) the perpetual calendar mechanism is constructed on an additional plate that sits on the dial side of the mainplate. In the cal. 5133, the perpetual calendar mechanism – which in the traditional construction has three distinct layers – is compressed into a single layer, and then set into a complicated recess, milled into the upper/top plate/movement side of the movement. Just how little extra headroom this adds can be seen when you look closely at the perpetual calendar – you can see the four ruby rollers that carry the automatic winding rotor, projecting through oval holes in the mainplate.
You’ll also notice that AP changed the configuration of the 48 month program wheel – the steps are curved, in order to allow for more secure engagement of the beak of the switching lever, although the family relationship between it and the 48 moth program wheel in the Lange grand comp is obvious.
Now let’s look at the 7138.
One of the biggest differences between the 5133 and the 7138 is the base caliber. The 7138 is built on the AP caliber 7121, introduced in 2022. This movement as a base caliber is 29.6 mm 3.2mm, which is only slightly thicker than the 2120 – 28mm x 2.45mm, without date or center/small seconds; with date, the movement becomes the 2121, and is 3.05mm thick. With the perpetual calendar mechanism in place, the 7138 is 29.6mm x 4.1mm, making it thinner than the 5134 (although still not as radically thin as the 5133).
The setting procedure from the crown, and the associated mechanisms, are visible in this short video provided by AP.
The first position of the crown is for hand winding and engages the mainspring barrel, located on the upper right. The second crown position switches the date hand, which you can see moving in the video when the crown rotates clockwise; you can also see the equivalent of the traditional grand lever, rising and descending each time the date switches, although the 48 month program wheel doesn’t rotate (as it should not, as you’re switching the date, not the month).However, if you rotate the hand in the second position counterclockwise, the 48 month program wheel will rotate and the month and leap year indications (at 3:00, right next to the crown) will switch.
When the crown is pulled all the way out to the third position, the hands can be set to the correct time.
Now comes the clever bit (not that the other bits weren’t clever). If you push the crown from the 3rd position back into the 2nd position, a clutch engages the crown with the moonphase disk and the day of the week hand; the day is set by turning the crown clockwise, and the moonphase, by turning the crown counterclockwise.
You’ll notice, by the way, that there is a 24 hour hand inside the day of the week indication. That’s there to show you where the “safety zone” is, which is indicated in red. This shows the time period during which, to prevent damage, you aren’t able to set the date – you can move the crown out to the setting position but you won’t be able to change the date until the 24 hand moves out of the safety zone.
The New 150th Anniversary Perpetual Calendars
The new movement is launching in three new watches. The two Royal Oak models are references 26674ST and 26674SG, in stainless steel and “Sand Gold.”
The Code 11.59 model ref. 26494BC is 41mm x 10.06mm, and cased in white gold.
The view through the caseback shows the caliber 7138, with its distinctive symmetrical balance bridge and mainspring barrel bridge. This is the one aspect of the watch which makes me feel a little blue personally – I’m never not going to miss the quirky but beautiful construction of the 2120 and the movements based on it, and I’m never not going to miss its history either, or the fact that to this day, despite the fact that it launched in 1968, it remains the thinnest full rotor automatic movement ever made. The fact of the matter is, however, that the 2120 in this the year 2025, shows its age in some respects. For one thing, the date version, the caliber 2121, doesn’t have a quickset date. For another, it’s a movement requiring special training for the watchmaker to service and repair, and it does have some engineering idiosyncrasies – for one thing, it has a “hanging” mainspring barrel, with no balance bridge (a not unusual engineering decision for an ultra-thin movement) and the single pivot for the mainspring barrel runs in an unjeweled hole in the mainplate. If the hole wears enough, the entire mainplate might need to be replaced (although I suppose a competent watchmaker might be able to press a bushing into place).
I said at the outset that the art of watchmaking in general, and the art of complicated watchmaking, are the arts of incremental improvement with sometimes diminishing practical returns in exchange for exponential increases in complexity and cost. However, this in no way diminishes what AP has accomplished with the caliber 7138. This is I think, almost certainly the most user-friendly mechanical perpetual calendar to date. The practical advantages are viewed in a certain light, incremental but at the same time nobody has ever come up with a really practical solution to greater ease of setting a perpetual calendar – at least not without other drawbacks. AP still has technical chops to rival any other fine watchmaking brand in the world, as we saw last year with the launch of the Code 11.59 RD#4 Universelle, and its first new releases for the 150th Anniversary show that for all some of its collabs get a disproportionate amount of ink, and raise some eyebrows, for their juxtaposition of fine watchmaking with popular culture, the fine watchmaking side of AP’s identity is as strong as it has ever been.
The 150th Anniversary Royal Oak Selfwinding Perpetual Calendar Limited editions: in sand gold, ref. 26674SG.OO; in stainless steel, ref. 1320SG.02. Cases, 41mm x 9.5mm, water resistance 50 meters, sapphire crystals front and back. Limited editions of 150 pieces world wide; prices, CHF 109,300 (Steel) and CHF 130,000 (Sand Gold).
The 150 Anniversary Code 11.59 Selfwinding Perpetual Calendar, ref. 26494BC.OO.D350KB.01: case, white gold, 41mm x 10.6mm, water resistance 30M. Sapphire crystals front and back. Limited edition of 150 pieces world wide; price, CHF 109,300.
Movement, all three watches: AP caliber 7138, selfwinding perpetual calendar, 29.6mm x 4.1mm, 422 components, running at 28,800 vph in 41 jewels with 55 hour power reserve. All calendar indications, and moonphase, can be set individually from the crown.
Find out more at AudemarsPiguet.com.