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Review: Jaeger-LeCoultre Master Ultra Thin Squelette

If I were to ask you to guess what the most universally interesting thing about watches was, what would you say? Investment? Diamonds? Branding? All those things are indeed very popular, but there’s something else in this bizarre industry that seems to capture people’s attention like nothing else: thinness. The thinnest watches in the world draw crowds like you wouldn’t believe to marvel at the incredible complexity and delicacy of mechanical watches that are barely thicker than a credit card. Piaget, Bulgari and now Richard Mille have all been hot on the ultra thin game, using more and more bonkers ideas to squeeze out an extra micron. But before all that there was this: the Jaeger-LeCoultre Master Ultra Thin Squelette—and it’s still incredible.


The Jaeger-LeCoultre Master Ultra Thin Squelette is no longer the thinnest watch in the world, but at just 3.6mm—bump that up to 4.73mm if you want the gem set version you see here—it still puts in a pretty good show. It’s a ways off the 1.75mm thick Richard Mille RM UP-01, but then again so is the year 2015 when it was first unveiled.

But here’s the thing: the current crop of paper-thin timekeepers have to play all sorts of clever tricks to get their size zero looks. From separating crown functions to using the case back as the movement baseplate, the watchmakers at these brands have turned engineer in order to come up with crazy but clever ways to ditch superfluous material.

And that’s the difference with this Jaeger-LeCoultre Master Ultra Thin Squelette. It doesn’t lose the case back or split the crown. You can very much see that it is built in the traditional vein of a mechanical watch. There’s a case back, a case front and a movement sandwiched in the middle. In many ways, that makes it even more impressive. What makes it unbelievable, however, is that this wasn’t just the thinnest watch in 2015—Jaeger-LeCoultre’s calibre 849 has been the heart of the world’s thinnest watches since all the way back in 1975.

Jaeger-LeCoultre has always had a bit of a thing for breaking records. Really, it’s a little bit of a show off. Given that Antoine LeCoultre literally invented the tool to measure a micron in 1884, it stands to reason the watchmaker has spent its time since proving the benefits of that work. In 1929—nearly a hundred years ago—Jaeger-LeCoultre announced the calibre 101. It was, and still is, the smallest movement ever made, 14mm in its longest dimension, 4.5mm wide and 3.4mm tall. It is no exaggeration to say that it could be easily swallowed.

For Jaeger-LeCoultre, making the calibre 101 was simply—said tongue-in-cheek of course—a matter of taking the basic components of a movement and stacking them into two layers. To make the thinnest movement, however, required a lot more thinking.

It was simply a matter of precision, taking a further 46 years to develop the capability to make parts thin enough to work. When metal starts getting very thin it does all sorts of strange things, warping and bending as the unseen stresses hidden within the atomic latticework overcome the torsional strength of the thickness—or lack of it.

The calibre 849 was and still is made up of 123 components across a 20.2mm span, crammed into a space just 1.85mm thick. It looks like a perfectly ordinary watch movement in its execution, with the exception of being very small and very thin. All that’s needed either side of it is hands and a case, and in 2015, that’s exactly what Jaeger-LeCoultre did to become the proud creators of the thinnest watch in the world.


But of course Jaeger-LeCoultre didn’t just settle for that. That would have been way too easy. See, this isn’t just the calibre 849, it’s the calibre 849 SQ, which stands for Squelette. No, that’s not those little electric cars you race around a plastic track, it’s the art of a removing as much material from a movement as you possibly can. Why? Well you would be forgiven for thinking it might be to aid lightness in a very Colin Chapman-esque way, but no.

It's for the complete opposite reason. Not to make it heavier, don’t be daft—but to make it prettier. To make an object lighter is to improve it practically, but there is absolutely no practical reason to skeletonise a watch like this, except to—once again—show off.

And it’s worth showing off. Watchmakers have been doing it since the 1700s to prove their merit in the courts of the kings. Keen to outdo their rivals, they would open up the layers of hidden mechanical delight inside their clocks to reveal where 90% of their efforts went. And I don’t blame them. Imagine spending many hundreds of hours making something only to hide all of it inside a metal box. Skeletonisation is where it’s at to best utilise the writer’s adage of show, don’t tell.

Things are a little different these days, however. Back then, a watchmaker would drill a hole into the material to be removed, thread a handsaw through and cut out every last piece by hand. These days, however, the rough work can be done by EDM—that’s Electrical Discharge Machining, not Electronic Dance Music in this case—leaving just the finishing for the human touch.

It makes sense really, because cutting out the chunks in-between isn’t necessarily hard, it’s just laborious. What is both hard and laborious is the hand finishing of what’s left. Combine engraving with bevelling and polishing and you’ve got yourself a lot of very fiddly work on your hands that could, with one lapse of concentration, be game over and in the bin.

The work is more than doubled over a traditional movement because the skeletonisation reveals so many more edges. Where the balance cock would have had just one outer edge to bevel and polish, now it has two more continuous inner edges as well.

There’s very little that doesn’t get this treatment, and perhaps even more impressive than the work that’s been achieved here is that fact that the calibre 849 can take it. Imagine that, the calibre 849 being constructed to tolerances fine enough to make it the thinnest movement in the world—and then when over half of that structural material is removed, it’s still fine. You would think it would become too weak and floppy and need beefing up a little bit, but no. Thanks to clever thinking of the placement of the supporting elements, it remains exactly the same thickness as the standard version.

These days, this very traditional look isn’t exactly the most popular, but it is no less impressive than it ever was. To see a balance of effort between the engineering and artistic sides of watchmaking competing against one another so heavily without compromise is truly impressive. Jaeger-LeCoultre were so far ahead of the game it’s taken half a century, some of the finest minds and a little bit of watchmaking cheating to finally beat it.

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