Caliber OS.24

Lock, impulse, drop

Six times a second, three things happen in this order. They are the whole difference between a watch and a spring that unwinds in four seconds.

Lock

A pallet jewel holds a tooth of the escape wheel. The whole train stops. Most of every second is spent here, motionless.

Impulse

The balance swings back, the fork tips, and the escaping tooth pushes the pallet — one small shove to replace what the balance lost to friction.

Drop

The tooth clears, the wheel advances, and the next tooth falls onto the other pallet. Lock again. That gap is the sound you hear.

The going train

Five wheels between the mainspring and the balance. Each one turns faster than the last by a fixed ratio, and those ratios are what turn one long push into hours, minutes and seconds.

1. Barrel

   Holds the mainspring. A wound spring pushes hard and a spent one pushes softly, so everything after this exists to make an uneven push into an even one.

   One turn in eight hours

2. Centre wheel

   Carries the minute hand directly. Its speed is the reason a minute is a minute here rather than a setting.

   One turn an hour

3. Third wheel

   No hand, no dial function. It is here to step the speed up again without asking the centre wheel to carry a load it would wear against.

   One turn in eight minutes

4. Fourth wheel

   Drives the small seconds at six. This is the fastest wheel you can watch with the naked eye.

   One turn a minute

5. Escape wheel

   Meets the pallet fork. It is locked, pushed and released six times a second, and that release is the only reason a watch runs at a steady rate instead of unwinding all at once.

   Six turns a minute

The wheels above turn at their real ratios to each other, driven by how far down the page you are. The escape wheel does not turn: it steps, one tooth per release, because that is what an escapement does to it.