Video and content by Tim Mosso
In 2007, Jaeger-LeCoultre launched its Duomètre à Chronographe to universal acclaim. As one of the most original engineering concepts of the post-quartz era, the Duometre immediately joined the ranks of high horology's most discussed novelties of that year's SIHH. But the "Chronographe" model was only the beginning; in 2010, the Duometre became a model line in its own right with the launch of the Duometre à Quantième Lunaire.
Unlike the mono pusher "Chronographe," the 42mm rose gold Quantième Lunaire is a cerebral model whose dedication to pure chronometry appeals to the intellect rather than emotion. While the principle of the Dual Wing movement - a second drive train and mainspring barrel for the complication - seemed like a logical, if elaborate, solution to reduced amplitude when running a chronograph, these measures seem like overkill when applied to a simple date and moon phase tandem.
The key to JLC's engineering logic lies in the division of duties between the Quantième Lunaire's functions. Rather than splitting the dual drive trains between time and complications as in the chronograph, the Quantième Lunaire engages one mainspring barrel to drive both complications and time display; the second train and power supply serve the balance alone.
By dedicating an entire drivetrain and mainspring to the balance, its isochronism and amplitude are liberated from the energy-draining influence of the time, date, and moon phase mechanisms.
To optimize the potential of these refinements, Jaeger-LeCoultre endowed the Quantième Lunaire with a unique hacking/synchronization system. When the crown is pulled to the first detent, the flying seconds hand advances to the index at "0," and the seconds hand halts; pulling the crown to the second detent causes a reset hammer to fall on the center wheel cam within the movement. With both foudroyant and seconds hands zeroed, the Quantième Lunaire can be set to the nearest 1/6 of a second against a reference time.
Even the zero-reset function carried an additional nuance. When activated for precise setting, the synching mechanism does not halt the balance. In conventional watches with "hacking" or "stop-seconds" functions, the balance halts when the hack is engaged. By keeping the balance in motion throughout the setting process, the Quantième Lunaire avoids the loss of amplitude that results from conventional stop-seconds systems.
Beyond chronometry, the movement of the Duometre à Quantième Lunaire features extensive engineering refinements that grant it further distance from conventional movements. Both mainsprings must be wound for the watch to function, and when fully wound, the watch will run for approximately 50 hours. The free sprung balance oscillates at 21,600 VpH, and it employs a large polar moment as a substitute for outright beat rate in order to assure precision.
All 42 jewels and 374 parts of this caliber sit amid a set of bridges and plates crafted from "German Silver," or - since Jaeger-LeCoultre resides in French speaking Vallée de Joux, "Maillechort." The material is an alloy of nickel, zinc, and copper. The last is responsible for the soft golden glow that characterizes the calibers of all Duometre models, and it is a deliberate reference to the LeCoultre pocket watch era. As one of the rare calibers that was engineered and designed aesthetically in equal measure, the caliber 381 bears a strong resemblance to the experimental 1881 LeCoultre caliber 19/20 RMSMI that inspired the modern Duometre movement concept.
On the dial side, a grained silver base with skeletonized power reserve scales offers a downright baroque take on the basic dual-element layout pioneered by the 2007 chronograph. The dial at 10 o'clock features a moon phase, age of the moon, and date indicator; a pusher corrector on the case flank advances the date, and a dimple corrector between the top lugs advances the moon phase. Hours and minutes are displayed at two o'clock, seconds are anchored at center, and the flying seconds sub dial splits the power reserve scales. All golden elements are 18-karat rose gold to match the case. The skeltonized elements at the base of the dial amount to an overpowering design feature, and Jaeger-LeCoultre diplomatically offers the model with and without the evacuated sections.
As of 2016, the family of Duometre models now boasts the Spherotourbillon, Unique Travel Time, "Grande Sonnerie," a choice of four metals, two case sizes, and a number of métiers d’art models. Yet he Duometre à Quantième Lunaire, with more variants than any other model, arguably could be called its model line's mainstay. Unarguably, it remains the purest expression of its manufacture's dedication to precision as an end in itself.