The engine inside an accessible Swiss automatic watch, drawn part by part from the back, from the dial side and, enlarged, at the escapement where each tick happens. For each part: what it does, an everyday example, and what goes wrong.
26 mmAcross
28,800Beats an hour
38 hPower reserve
25Jewels
Back
As seen through a display case-back, crown on the left. The rotor covers the left half; lift it to see the winding wheels underneath.
Dial side
With the dial and hands removed, crown on the right. The date shows through the window at 3 o'clock.
The escapement, enlarged
Slowed 8 times, so 1 beat takes 1 second. The drawing is simplified to show the motion.
1. UnlockThe impulse jewel on the swinging balance knocks the fork, which pulls a pallet stone out of the escape wheel's way.
2. ImpulseFreed, the escape wheel pushes on the pallet stone, and the fork passes that push back to the balance to keep it swinging.
3. DropThe wheel jumps forward a fraction until a tooth hits the other pallet stone. This is the tick you hear.
4. LockThe wheel is held still while the balance swings freely to the end of its arc, turns, and comes back to do it all again the other way.
Every part
Numbers match the drawings. Under each name: the views it appears in.
Frame
Power
Automatic winding
Gear train
Regulation
Under the dial
About this drawing
An original drawing of a generic 3-hand automatic with date, the class of movement inside most accessible Swiss watches. It is not a copy of any maker's calibre: wheel positions, sizes and tooth counts are simplified, and the escapement is drawn for clarity rather than exact geometry.
Sources: the lever escapement (Thomas Mudge, 1754), shock protection (Incabloc, 1934), mainspring slipping clutches and silicon hairsprings from standard horological references; the chronometer limits from the COSC standard (-4 to +6 seconds a day).