The subdial on the left houses the normal hour and minute hands. These hands, together with a center seconds hand that is in continuous motion, and a power reserve hand (lower left), are gold in color to indicate their time keeping functions. In this example above, the time indicated by the golden hands is 1:50 and 22 seconds, and the power reserve is full (+50 hours).
The subdial on the right houses the chronograph minute and hour hands. The elapsed time of the chronograph function is read in the same way as the timekeeping hands – the short hand records the hours and the long hand the minutes. At the 6 o'clock position of this sub-dial is a tiny recording disc that rotates once every ten minutes. Its period of rotation is synchronized with the minute recording hand in order to eradicate any margin of error when reading the minute counter hand. Like the time keeping hands, the chronograph hands, together with the sweeping seconds hand at the center and the power reserve hand, are all of the same color – blue, to indicate their chronograph functions. In the same example, the chronograph has functioned for 2 hours, 20 minutes, 38 seconds. But wait, there's more…
There is a third sub-dial at the center lower portion of the main dial. This sub-dial houses the flying-seconds (foudroyante) hand that makes one revolution every second, giving a precise fractional indication of time accurate to 1/6th of a second!
Therefore, the chronograph shows an elapsed time of 2 hours, 20 minutes, 38 and 1/6th seconds.
The Duometre employs bi-directional winding since there are two power sources – one for the normal time function and another for the chronograph function. While you might not use the chronograph regularly, the normal time function is in constant motion and therefore power will need to be replenished at least every two days. Turning the crown in a clockwise direction winds the normal time function barrel (marked: HEURES/MINUTES above).
On the other hand, winding the crown in a counter-clockwise direction replenishes power to the chronograph function barrel (marked: CHRONOGRAPHE above) when needed. Notice that the same wheels are used to wind both the hours/minutes barrel and the chronograph barrel. You might ask why both barrels are not being wound when the crown is turned in either direction. On closer examination, you will see a ratchet wheel and two clicks at the center of each barrel. This allows one barrel to wind when the crown turns in one direction and the other to wind when the crown turns in the opposite direction.
I should point out that the chronograph function will not operate (even though it might be fully wound) unless the normal time function is operating since it is the latter that constitutes the heart beat of both functions as it contains the escapement.
