Why the escapement is the only part that matters

A mainspring stores energy. A gear train transmits it. A dial and a set of hands report a result. None of those parts decides anything.

The escapement does. It is the interface between a continuous force and a discrete count: a balance wheel and hairspring oscillate at a fixed rate, and on each half-cycle a pallet fork releases exactly one tooth of the escape wheel and then locks again. Charge, lock, release one step, lock. Eight times a second, for as long as the spring holds.

Why 28,800

Four hertz is a compromise. A slower balance is easier on the lubricant and the pivots; a faster one is less disturbed by the movement of a wrist and gives a finer division of the second. 28,800 alternations per hour sits where those two curves cross for a watch that is meant to be worn.

What you can see

Almost nothing, at normal speed. The lock lasts a few milliseconds. Slowed down far enough, the sequence separates into its parts, and it becomes obvious that the mechanism is not turning smoothly at all — it is being let go, one notch at a time.