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
In the first place, you wind the spring really tight, and only use a small fraction of its range. The difference between a 100% wound spring and a 95% wound one is only 5%, after all. But…
The spring that *powers* the watch, the mainspring, isn’t the same spring that causes the consistent timing; that’s called the *hairsping.* It causes the *balance wheel* to twist back and forth, and that’s what meters the time.
What’s basically happening in the watch is that the whole mechanism is under tension from the mainspring, wanting to fling the hour and minute hands forward; but a mechanism called an *escapement* only allows it to move one tick each time the balance wheel swings. (This is just a summary of how the watch works, for context, not an answer to your question.)
One of the things that happens when the escapement lets the movement advance is that the movement gives the balance wheel a little kick. But the mainspring is either wound-up enough to charge that kicking mechanism up, or it isn’t. So the boost that the balance wheel gets is always the same (or missing, in which case the watch is out of juice and needs to be wound).
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