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

Well the first trick is to use a *constant force spring*, which does what its name implies, or at least close to it. Then you pair that with a good *escapement* which is as insensitive as possible to variations in the driving force.

The advantage of an automatic watch vs one that needs to be wound is that it is constantly being wound, and so should stay near the same level of tension.