In 2007 Jaeger-LeCoultre launched the ground-breaking Duometre mechanism in the form of a chronograph – the complication that epitomises the concept of precision. In 2024, the Maison applies the Duometre concept in an entirely new timepiece, marrying the high precision of a chronograph with the charm of a celestial complication.
Powered by the new Calibre 391, the Duometre Chronograph Moon presents an intriguing contrast between the lightning-fast operation of the chronograph – which can time intervals as small as 1/6th of a second – and the slow rhythm of the moon as it passes through its cycle in 29.53 days, complemented by a night and day display.
Jaeger-LeCoultre presents the Duometre Chronograph Moon in two variations: A platinum case contrasting with a copper-coloured dial, and a pink gold case offset by the discreet elegance of a silver dial. Both models are enhanced by a hand-stitched alligator strap with small-scale alligator lining.
Solving the conundrum of complications
The fundamental problem of complex mechanical watches is that, for any complication to operate, it naturally draws on some of the power provided by the barrel. This disrupts the perfectly regular and constant supply that is required by the meticulously adjusted escapement to fulfil its timekeeping function as precisely as possible.
The search for a solution to this problem at Jaeger-LeCoultre during the early 2000s eventually led to the invention of the Duometre mechanism. Introduced in 2007 and patented by Jaeger-LeCoultre, it features two separate barrels and two independent gear trains – one to drive the escapement (for timekeeping) and one to power the complications – both integrated into a single calibre and linked to a single escapement. For the first time, it was possible to guarantee that the movement’s isochronism (the regularity of its ‘heartbeat’) is not compromised by the operation of any complication.
While the Duometre is revolutionary in modern watchmaking, the underlying principle had, in fact, been explored by the Manufacture more than 120 years earlier; the LeCoultre Calibre 19/20RMSMI was equipped with two barrels and fitted into a pocket watch in 1881. Because that calibre had only one gear train, it did not solve the fundamental problem; nevertheless, it provided a theoretical ‘trigger’ for the Duometre concept.
Jaeger-LeCoultre’s engineers and watchmakers chose the chronograph for the first application of the Duometre concept in 2007 as it represented the greatest challenge to accurate timekeeping posed by any complication because its operation requires short bursts of very high power. Since then, the Duometre mechanism has been associated with several other complications, including moon phases, travel time and a tourbillon.
An entirely new calibre
The open-working of Calibre 391 serves two purposes: Not only does it greatly enhance the aesthetics, it also serves a technical purpose, enabling the watchmakers to more easily assemble some parts of this highly complex calibre. This is a fine example of Jaeger-LeCoultre’s philosophy of marrying mechanics and aesthetics in such a way that each serves the other. Being a manually wound calibre, there is no winding rotor to conceal the chronograph levers.
Traditional Haute Horlogerie finishes abound: Crisply bevelled and polished angles define the edges of the bridges; brushed surfaces contrasts with polished metal; perlage on the main plate reflects light back up through the mechanism; and blue screws provide a pleasing contrast to the silvery tones of the metal.
A comfortable 42.5 mm in diametre, the case is a complex structure of 34 separate parts and the lugs are screwed rather than integrated to enable the use of multiple finishing techniques. A mixture of polished, brushed and micro-blasted surfaces creates a fascinating play of light with every movement of the wrist.