The gears of the stopwatches are housed, together with a part of the worm-threaded staff of the rotating disk, in a box one cm thick which is supported by two square columns fixed to the frame of the siren.
The rectangular plate representing the front of the stopwatch (6.9 x 4.4 cm in height) holds two round, silver-plated dials on one of which is a circular scale divided into 100 parts and on the other a scale with 50 divisions. The hand of the first dial is fixed to the shaft of a gearwheel the teeth of which can be made to engage the worm that moves the hand by one division for each rotation of the disk by shifting the entire supporting plate horizontally. The hand of the other dial is fixed to the shaft of a gearwheel with 50 teeth which is made to advance by one division for each complete rotation of the other hand by means of a lever joined to its staff. Thus on the first dial we read the number of rotations from 1 to 100 and on the second the hundreds from 1 to 50.
It is in a good state of conservation.