Geartrain slack, too, I believe. Easier to see this in a quartz vs. a full mechanical, because in a mechanical, the geartrain is under constant load (one reason why the bits are much bigger in a spring-powered watch). Not just slack in terms of having wide tolerance, in which the stepper could turn a few degrees and the hands not move at all, but also slack in that as soon as the stepper motor stops its little once-per-second fandango, the entire drivetrain is inert with no power going through it at all. However, the inertia of the second hand can cause overshoot - and sometimes you will notice the hand overshoot by a needle's width and then spring back to where it should be. I would attribute this to the effect of the magnet on the stepper, which "brakes" the second hand.Originally Posted by walkerwek1958
Some expensive quartz movements from Japan have a damping mechanism on the second hand to reduce the visible "error" that results.