The Jules Audemars Chronometer “ChronAP”

The Swiss lever escapement has enjoyed an industrial and intellectual hegemony unlike any other single invention in the entire history of watchmaking. Despite the fact that we call it the “Swiss” lever, the lever escapement was invented by an Englishman. Thomas Mudge was a guy with an extremely unglamorous name, who was himself not an especially glamorous looking individual — in a portrait made during his lifetime, he looks like a kindly parson from a Regency novel — and he is supposed to have invented the lever escapement, or, at the very least, to have adapted the clock anchor escapement for use in a watch, in or around 1754 or 1755.

The lever escapement has been with us in one form or another ever since, although it took quite a while for it to supersede other escapements entirely. Breguet used the lever, but also the detent escapement (also called a “chronometer” escapement as it was frequently used in marine chronometers) as well as the cylinder escapement. The cheap pin-pallet escapement made inexpensive mass produced watches possible in the late 1800s (and was the escapement used in the so-called “dollar” watches in the United States — no prizes for guessing where the name came from). And the Ancient Of Days, the verge escapement — the first mechanical escapement known — hung on until the beginning of the 20th century.

The lever, however, triumphed over all other escapements and today, if you own a mechanical watch, odds are almost 100% that it has some variation on the lever escapement inside. The only escapement to have been successfully commercialized and put into large volume series production other than the lever is the co-axial escapement, and the enormous challenges involved in making the transition from hand-tuned bespoke construction to mass production speak to the problems involved in creating an escapement that really improves on the lever, especially without creating other problems.

That it is hard, however, has not stopped people from trying. I am reminded of a parody of JFK’s famous line, “We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard,” — in the case of improved escapement design you might say, “We do these things, not because they are easy, but because we didn’t realize how hard they would be.” In the last 20 years, there have been many, many attempts to produce improved escapements — a lot of them based on silicon technology — but most of them have ended up getting no further than a late prototype stage (I think, in no particular order, of the Zenith Defy Lab, Parmigiani Fleurier’s Genequand Oscillator and the late, great (well, I thought it was great) Girard-Perregaux Constant Force Escapement.)

If you leave out silicon based solutions (which include Ulysse Nardin’s escapements based on Breguet’s echappement naturel, as well as the Frederique Constant Slimline Monolithic) then the field really starts to narrow. As a confirmed materials science conservative (in other words, a technical retro-grouch) I personally feel like there’s something very attractive about using, as much as possible, traditional watchmaking materials to solve traditional watchmaking problems. This is a bit of a slippery slope because if you really want to let your retro-grouch flag fly, your greatest praise would be reserved for watches whose movements use only brass (with whatever plating you prefer but mercury gold gilding has a fine antiquarian vibe, plus of course, neurotoxicity), steel and jewels for things like pivot bearings, impulse jewels and lever pallets, and you would look askance at modernist aberrations like Nivarox balance springs (you would probably also happily rail against things like wire erosion and LIGA manufacturing techniques but that is a rant for another day).

One of the very, very small number of experimental escapements trotted hopefully out into the light of day over the past 20 years, was produced for a few years by Audemars Piguet. AP is today pretty much synonymous with just the various Royal Oak and Offshore models but it was not that long ago when it rolled out technical innovations on a regular basis (to be fair, it still does occasionally — there are the various RD watches, including most recently, the Code 11.59 RD#4 Supercomplication) and, in the mid-2000s, there came from Audemars Piguet Renaud & Papi a most unusual and most interesting escapement.

If you want to do the lever escapement one better, there are a couple of problems that you need to address. The first of these is that lever escapements rely on the sliding friction of the escape wheel teeth across the jeweled pallets of the lever to transmit energy to the balance. This sliding friction requires oil and, since all lubricants deteriorate over time (renewing aging lubricants is the single biggest reason it is not such a hot idea to run your watch forever without getting it serviced), the precision of any lever watch is apt to, sooner or later, deteriorate as well.

The second problem, which is less well known, is that the geometry of the lever escapement doesn’t make for very efficient energy transmission. Only about 30% of the energy that reaches the lever gets passed on to the balance, which is sort of a hair-raising figure the first time you encounter it.

The advantages to the lever escapement are considerable, however. For one thing, it is very resistant to shock (specifically, it is not apt to unlock easily if the watch gets a jolt, which is a problem with the chronometer escapement and the major reason the chronometer escapement has not been widely adopted in wristwatches). It is also self-starting. In an unwound state, the balance sits in its neutral position with the lever held away from the escape wheel teeth and when you wind a lever watch, at some point the escape wheel starts to turn, its teeth begin to interact with the lever and the watch starts ticking.

Finally, it can be, if carefully made, extremely precise. It takes a little doing but you can make lever watches which consistently out-perform COSC chronometer standards (Rolex makes a million watches a year which do precisely that). It doesn’t hurt, by the way, that the lever escapement has been around for several hundred years.

The most successful attempt so far to overcome the basic problems of the lever escapement, at least in mass produced timepieces, is the co-axial escapement (as used in a very refined form by Roger Smith, and also in a configuration very advanced from Daniels’ original design, by Omega). While Omega has taken advantage of modern materials solutions as well (a silicon balance spring, for instance) it is not strictly speaking necessary to use advanced manufacturing or materials to make a co-axial escapement work. As designed by George Daniels, the co-axial escapement requires no lubrication on impulse surfaces, is self-starting, and can produce very precise performance; perhaps its only major disadvantage is that it is very complex.

Audemars Piguet’s experimental escapement, like the co-axial, was partly influenced by a much earlier escapement designed by Robert Robin around 1790. The Robin escapement was an early attempt to combine the benefits of the lever and chronometer escapements and it was not entirely successful (Breguet used it occasionally, in clocks and around a dozen watches, including a tourbillon — no. 1297). The Robin escapement uses a lever with jeweled pallets, but these are passive — they are there only to lock the escape wheel and impulse is transmitted to the balance directly, by the escape wheel, just as in the chronometer escapement.

AP’s escapement is in principle very similar to Robin’s but with several improvements intended to better adapt it to a wristwatch. Robin’s escapement had a couple of problems – one was its complexity, which required extreme care and precision in manufacturing, and the other was that it was easily unlocked by accident. AP’s escapement, which was introduced in 2006, was, like the Robin escapement, constructed so as to allow the escape wheel to impulse the balance directly, as in a chronometer escapement. To solve the problem of accidental unlocking, AP included a safety roller on the balance, which would only allow the escapement to unlock when it was supposed to, and they ran the balance at a very high frequency — 43,200 vph, versus the standard 28,800 vph for most modern mechanical watches; I think this might be a record for high frequency in a production watch that doesn’t use silicon components. And, the AP escapement was much more efficient than the lever, by about 20 per cent.

The AP direct impulse escapement, like the Robin, gives impulse in only one direction but at a high enough frequency to obviate, at least to some degree, the issues inherent in having a single-impulse escapement in a wristwatch (a double impulse design like the lever is more resistant to disturbances). The AP escapement like the Robin was still not self-starting — I remember asking Giulio Papi, one of the founders of Renaud & Papi, about the issue when the escapement was launched and he grinned and made a gesture you’d make if you were shaking a watch to get it running. The movement was first introduced in one of the most impressive watches of the 2010s — the Audemars Piguet Tradition d’Excellence No. 5, which was a limited edition of 20 pieces.

The escapement seemed very promising and Audemars Piguet produced it in a larger series, but still in very small numbers, in the watch you see here: the Jules Audemars Chronometer, nicknamed the ChronAP. It’s a very unusual watch — the escapement and escape wheel, as well as the double balance spring, are on the dial side, along with a sub-dial for the hours and minutes hands, another very prominent one for the seconds hand (which at 43,200 vph would look to the unaided eye as if it were running smoothly around the dial) a power reserve indicator (72 hours), and the two large mainspring barrels on either side of the dial for the time. It’s a large watch as well, at 46mm in diameter, which gives the architectural design (somewhat reminiscent of a Breguet Tradition) quite a lot of room to spread out. The mainspring barrels, ratchet wheel, and train wheels are visible on the movement side of the watch, and the quality of finishing is extremely high and, despite the advanced escapement design, very traditional (there are sixteen sharp inner corners on the cocks holding the train wheels in place, for instance). Though the watch is large, the movement, at 40mm, is a good fit for the case.

A version of the watch in a white gold case even won the prize for Best Men’s Watch at the 2009 GPHG. AP has not, however, chosen to keep a watch with the escapement in production and I can only speculate as to why not. It may be that the complexity of the escapement and the costs associated with tooling up for a larger production run simply weren’t worth any advantages in performance gained, and it may be that the fact that the escapement was still not self-starting may have hurt its chances for broader acceptance as well — at this point, it’s anybody’s guess. Running a mechanical escapement at that high a frequency may have had issues over the longer term which were not apparent during prototyping. But, for all that, the Jules Audemars Chronometer (yes, the watches were all certified as chronometers by the COSC) represents a kind of high point in modern watchmaking — an era in which inquisitive minds were, in unprecedented numbers, considering how to make escapements that would represent definitive improvements on the venerable lever. As a piece of watchmaking history, as well as a piece of very high quality traditional craftsmanship, the ChronAP was then and is now, a most remarkable watch.

Not one you’ll see on just anybody’s wrist at your next enthusiast meet-up, either.