The Sphérotourbillon is one of Jaeger-LeCoultre‘s finest inventions, together with the Gyrotourbillon. We’ve already covered it in a previous article about the Duomètre à Spherotourbillon. This watch is based on two major innovations, both included in its name: the Duomètre and the Sphérotourbillon.
The Duomètre, or dual wing concept: Not so long ago, making a traditional caliber reliably that could handle an additional complication as well as indicating the time implied the risk of jeopardizing the precision of the movement’s operation. Every additional complication (meaning everything that is not directly linked to the hours, minutes, and seconds) affects timekeeping because of additional forces required to actuate levers and gears. Even a simple date disk needs those elements. The changing of the date is activated by gears or levers, which make the date wheel or date jump. To make the date wheel or pointer-date hand jump, some force is needed. In a small mechanical movement, these forces are relatively large — so large that they will effectively cause the watch to temporarily suffer a drop in precision, during the complication’s activation.
What Jaeger-LeCoultre did was to create two separate gear trains and mainspring barrels, each driving a part of the watch: one to drive the time and one to drive the complication. This way the “time-indicating part” of the watch runs free of negative influences. Of course, most of the indications are linked to time — a date might change at midnight, a moon-phase is regulated by the days and months — so we might have two gear trains, but both are connected by a shared regulating organ.
As for the Sphérotourbillon: The regulating organ is a special type of tourbillon, also known as bi-axial tourbillon. As well as revolving around the axis of its carriage, the tourbillon also spins around a second axis, inclined at a 20° angle. The combination of these two distinct and fast rotations (respectively 30 and 15 seconds per revolution) provides much better “protection” from negative gravitational forces than any standard tourbillon. Also note that the Sphérotourbillon comes with a specific cylindrical balance-spring.
What does all of this mean for the new Jaeger-LeCoultre Duomètre Sphérotourbillon Moon? The dual wing concept here means that one mainspring and gear train is driving the hours, minutes and seconds (located in a subdial at 6:30) and a second mainspring and gear train is driving the moon-phase indicator, located here inside the main dial. Both mainsprings are linked to their own power reserves (at 1:30 and 5:30). When fully wound, the watch will run for 50 hours.
The moon-phase is extremely precise on the Duomètre Sphérotourbillon Moon; when it is properly adjusted, it is designed to remain accurate for a full 3,887 years. Another technical feature is linked to the precision and adjustment of the watch. Instead of having a classical hacking seconds mechanism, the movement of this Duomètre Sphérotourbillon comes with a sort of flyback to reset the second hand to zero, with the help of a pusher located at 2:00. When pulling the crown, the balance wheel remains active and the watch thus remains accurate even when adjusting the time to the nearest second.
The Jaeger-LeCoultre Duomètre Sphérotourbillon Moon comes in a 42 mm x 14.3 mm case made of 18k white gold, with a grained silvery-white dial. Around the Sphérotourbillon at 9:00, we can see a superb “stairway” made of non-treated nickel silver with a satin finish, just like the mainplate and bridges of the movement, all of which are, of course, decorated by hand.
This extremely complicated and highly appealing watch will be limited to 75 pieces.
- Movement: Duomètre Sphérotourbillon Moon; Mechanical manually-wound movement, Jaeger-LeCoultre Caliber 389, crafted, assembled and decorated by hand; nickel silver bridges and mainplate; two barrels, 50-hour power reserve; 476 parts, including 56 jewels: 10.45 mm thick; 33.7 mm in diameter
- Sphérotourbillon: 105 parts; tourbillon carriage in grade 5 titanium; total rotation speed = 30 seconds for a complete turn; two combined movements; carriage axis rotation speed = 15 seconds for a complete turn; carriage rotation speed = 30 seconds for a complete turn; tilt of the carriage = 20°; diameter of the carriage = 11.50 mm; weight of the carriage = 0.518 grams; 14k gold balance wheel with 14k gold eccentric inertia-blocks; inertia = 12.5 mg.cm2; frequency = 21,600 vph; cylindrical balance spring
- Functions – Hours, minutes and small seconds with flyback function; two power reserves, one for the regulating organ and one for the functions; moon-phase indication with one day of deviation every 3,887 years; 24-hour indication; Sphérotourbillon