During my recent JLC boutique visit I viewed many beautiful timepieces. And as I promised, here is my favorite – the Jaeger-LeCoultre Duomètre.
In most chronographs the “timekeeping” and “chronograph” functions, share the same power source. So when the chronograph is used, the timekeeping accuracy can be affected. To improve the chronometric efficiency of the “timekeeping” function, Jaeger-LeCoultre engineered two separate power sources (and gear trains.) One for the “chronograph” (stopwatch) and one for “timekeeping” (seconds, minutes and hours.) This eliminates the typical power loss that occurs when the chronograph is in use. In fact, up until now, two separate power reserves were only available on extremely complicated Sonnerie timepieces.
On the left, a subdial displays the timekeeping hours and minutes (platinum hands). Timekeeping seconds are displayed through a platinum central seconds hand. And the timekeeping power reserve is displayed on the lower left, with a platinum hand.
On the right, a subdial displays the chronograph hours and seconds, with blue hands. A small indicator window displays the minutes (at 6 o’clock on the right subdial). The chronograph power reserve is in the lower right, in blue as well.
JLC ingeniously varied the hand materials based on their function. All the blue hands are part of the “chronograph” function and all the platinum hands are part of the “timekeeping” function.
Then what does the blue handed subdial at 6 o’clock represent?
The dial at 6 o’clock, makes a full rotation every second. This is a foudroyante or flying seconds function and allows the chronograph to read times, accurate to 1/6th of a second. And believe me, if you haved seen a flying seconds function, you are missing out. It rotates around the entire subdial once per second, this is incredibly fast and awesome to watch.
There is more though. Instead of using a coupling-clutch, the chronograph function is actually operated by the jumping-seconds mechanism. The same mechanism that allows precise one-sixth second accuracy. It also allows the use of a single push-piece to control and synchronize all five counters. Including the minute-unit counter – a watchmaking first, for which Jaeger-LeCoultre has filed a patent.