How do mechanical (automatic) watches keep time exactly when springs exert different amounts of force depending on how tightly wound they are?

Question

I know that mechanical watches have a spring that they wind to store energy, and un-winding the spring produces energy for the watch. But a spring produces a lot of force when it’s very tightly wound, and very little when it’s almost completely un-wound. So how does the watch even that out with high precision?

In: 95

Answer 1

In short, the accuracy gets worse the more the mainspring winds down. There are some types of constant force escapements or drive systems that fight this but on rare more expensive watches.

For example in a chain drive watch (fusee & chain) the chain gets unwrapped and wrapped on sprockets of varying diameters similar to a CVT gearbox which equalizes the torque.