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From a physics angle we're mostly dealing with electromagnetic induction. Faraday's law of electromagnetic induction states:

"that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux".

The magnetic field here is attached to the glide wheel (rotor). The conductor is some stationary spools placed near the glide wheel. This means the voltage output depends on how fast the glide wheel spins (rate of change of the flux).

The other part of Springdrive comes from Lenz’s Law of Electromagnetic Induction:

"the direction of an induced electro magnetic field is such that it will always opposes the change that is causing it"

That means that the current creates a electromagnetic field of its own that opposes the changes in the magnetic field that caused it.

So that opposing field depends on the rate of flux according to Faraday. That rate of flux directly correlates to the passage of time (the spinning of the glide wheel).

By adjusting the placement and configuration of the circuit (the spools) we can influence the flux, thereby influence the induced voltage, thereby influence the induced magnetic field that opposes the change that is causing it, which is the spinning of the rotor that correlates to the passage of time, to a degree that hopefully is around 1 second per second (or 1 rotation of the glidewheel per 1/8 second).

Note that if the glide wheel accelerates for some reason, the change of flux changes, the voltage changes, and the opposing magnetic field increases, forcing the speed of the glide wheel down. On the other hand, if the glide wheel slows down, the opposing magnetic field decreases and allows the glide wheel to spin faster.

So technically the "smooth" second hand isn't smooth at all, but slows down or speeds up about 8 times a second, so it's not exactly "at a constant speed," but since it's not a start-stop motion, it sure looks smooth to an observer.

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