It's kind of a tough time to be a tourbillon. Complications generally have at least a little bit of an air of let-them-eat-cake about them (okay, probably not the chronograph), but they can often get away with it for different reasons. Chiming complications can plead the undeniable craft which, even today, it still takes to make one; perpetual calendars can argue their connection to the cosmic rhythms of the Earth's rotation and its annual journey around the Sun; the rattrapante chronograph can play the craft card (at least in its most classic version) and its greater utility than a standard chronograph. But the tourbillon? It's long since been generally conceded by even its most ardent fans that you don't need a tourbillon to get a more accurate watch. A lot of folks would argue that, strictly speaking, it's not even a complication, inasmuch as it doesn't display any additional information. Which is as good a rough and ready description of a complication as any – though it leaves out a lot of watchmaking which is indisputably complicated to do, including ultra-thin watchmaking. Fake Watches

Still, tourbillons continue to fascinate watch enthusiasts and watchmakers alike – no less a master than Roger Smith has gone on record as saying he'd like to make one – and given the number of tourbillons of all kinds released every year, it's clear that folks are still very much interested in owning them as well. As with most mechanical watchmaking, how you do it is at least as important nowadays as what it is you do, and a well-made tourbillon is still not only interesting to look at, but also a legitimate demonstration of watchmaking as an art as well as a technical exercise.

Jaeger-LeCoultre's new Master Ultra-Thin Tourbillon Moon is a quite beautiful example of the genre, with some interesting additional technical features which help distinguish it from the rest of the crowd. The full-rotor tourbillon movement is a relative rarity – JLC caliber 983, which looks to be the JLC cal. 973 automatic tourbillon, but with the addition of a moon-phase and date indication. The date indicator is a centrally mounted hand, which has a neat little trick up its sleeve (one we've seen before from JLC), which is that at midnight on the 14th, it jumps from one side of the aperture for the tourbillon to the other, landing on the 15. This is to keep the date hand from partially obscuring the view of the flying tourbillon (and it gives owners a reason to stay up until midnight on the 14th, too). The main moon-phase display shows the Moon as seen from the Northern Hemisphere, but there is also, around the main display, a double-sided hand that shows the moon-phase in the replica rolex Southern Hemisphere on the left, and the age of the Moon on the right.

This is a complicated tourbillon in a pretty classic idiom. The round, rose-gold case is 41.5mm x 12.10mm. That does not, at first, sound particularly thin these days – not with the number of extremely flat tourbillon movements that have debuted over the last decade or so (and culminating, of course, with the Bulgari Octo-Finissimo Tourbillon Automatic). The case alloy is JLC's proprietary Le Grand Rose alloy, in which a small amount of palladium is added to help resist corrosion and discoloration. (Rose-gold alloys stabilized with metals from the platinum group have become increasingly popular in the watch industry since the introduction of Everose by Rolex in 2005.)

However, it helps to keep a few points in mind. The calibers 983 and 973 are full-rotor self-winding tourbillons – this is a surprisingly rare sub-genre in the world of automatic tourbillons which have tended, especially as the race to produce extra-flat tourbies heated up, to have either micro-rotor (the Piaget caliber 1270P) or peripheral rotor designs (Bulgari, Breguet). There are other full-rotor tourbillons – most recently from Audemars Piguet in the Code 11.59 collection. AP's Code 11.59 Flying Tourbillon uses the central rotor caliber 2950, and it's the first time AP has had a central rotor flying tourbillon in its collection – in a watch which, with no complications, comes in at 41mm x 11.80mm.  

A full-rotor design is always going to be thicker than a micro-rotor or peripheral rotor design, and the JLC manages to be just 0.30mm thicker than the Code with the addition of the moon-phase display and date. That said, I don't think this watch is going to necessarily make anyone emit a low whistle of wonder at its slim profile, but considering the fact that the very flattest automatic tourbillons, with peripheral or micro-rotor winding systems, are roughly 5-7mm affairs, a 12.10mm-thick full-rotor complicated tourbillon ain't too shabby.