The escapement is a very, very clever thing. The gears of a watch only rotate in one direction. The oscillator, however, swings in two directions – God willing, it takes about the same time to make every swing, otherwise you don't have a timekeeper. The escapement has to do two things at once. It has to pass energy from a gear turning one way, to a balance swinging two ways, and it has to count each oscillation.
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