This compteur works on the same principle as today's chronographs in that it has start, stop and reset functions. However, it does differ in one respect – the push-piece (1) on the pendant that starts the instrument must be held down in order for the hands to turn. To stop the device, the user just needs to release the push-piece. Moinet therefore designed a pin that could be inserted into the pendant from the side (as shown in figure 28) and that would allow the user to measure long periods of time.
The push-piece was thus held down until the pin was removed and the instrument could be used for as long as there was sufficient energy for it to function.
From left to right we have 2 levers and a spring, all of which are operated via the push-pieces:
Reset lever for the thirds hand
The start/stop lever and return spring are shown in figure 29 and the reset lever in figure 31.
Before describing how the instrument works, we should also highlight two other features of the mechanism. The first of these is the arm on the escape wheel, indicated by a red arrow in figure 30. Similarly, there are two arms beneath the foliot (indicated by the red arrows in figure 31).
The lever under the wheel is used to reset the instrument.
The two arms beneath the foliot are used to stop the instrument from operating. Push-piece 2 Fig. 28 Start/stop lever Return spring Push-piece 1 Fig. 30 Fig. 29 Push-piece 1 Locking pin 21
Timing thirds! Push-piece 1 Start/stop Reset lever Fig. 31 Fig. 32
FUNCTION 1: START
In figure 32, we can see that the reset lever is positioned in such a way that the train is free but locked by the start/stop lever, which blocks the foliot (beneath the balance-spring, as shown in figure 32a).
When push-piece 1 is depressed, it pushes on plate P (indicated by the arrow beside push-piece 1 in figure 32 and in more detail in figure 32b).
At one end of the plate is arbor T, which acts as a pivot for the plate and ends in a square.
The start/stop lever fits onto this square via a square hole in its base (cf. Fig. 29). The other end of the lever is bent at an angle and locks the foliot (Fig. 32a).
At the other end of the plate is the trapezium-shaped block Z (Fig. 32b), which protrudes above the plate and makes contact with the end of the return spring (Fig. 32c).
Fig. 32b Return spring Push-piece 2 Reset
Fig. 32a Fig. 32c
The arrows in figure 33 indicate which way the levers move when push-piece 1 is depressed. We can therefore surmise that the stop lever releases the foliot, setting the train in motion, and that the trapezium-shaped part slides against the return spring. The hands will continue to turn for as long as the user holds the push-piece down.
FUNCTION 2: STOP
To stop the instrument, the user simply has to release push-piece 1. This causes the stop lever to return to its original position where it blocks the foliot, as shown by the blue circle in figure 35.
This return action is caused by the return spring pressing against the trapezium-shaped part, as shown in figure 33a. The elapsed time can be read on the dial. The hands will not move unless the user depresses push-piece 2.
FUNCTION 3: RESET THIRDS HAND
To understand this function, we need to go back to figure 30 and compare it with figure 34. We can see that push-piece 2 presses on a part with an upper pivot located next to the part labelled 'curved plate'. We can gain a better understanding of this function by removing the all its moving parts and adding others (Fig. 35).
When the user depresses push-piece 2, it pushes on the curved plate, causing two consecutive actions:
1) The curved plate moves in the direction of arrow 1), releasing heel T1 of the reset lever at end E. Spring R pushes on heel T2 of the reset lever, causing heel T2 to move in the direction of arrow 2. The other end of the reset lever (circled in red) then moves above the escape wheel, as shown in figure 35. However, the train still cannot turn as it is locked by the stop lever, which is blocking the foliot (see blue circle).
2) If push-piece 2 remains depressed, the curved plate continues to pivot, causing end E to hit plate P, which supports the stop lever. Plate P then moves in the direction of arrow 3, causing the stop lever to move in the direction of arrow 4. The foliot is released and able to resume its oscillatory movement once more. However, the reset lever is now in the path of the arm, locking the escape wheel (see red circle) and the thirds hand is set at zero, as positioned by the watchmaker.