Why does the second hand of a quartz clock move in jerks?

            The seconds hand of both quartz and spring watches move in jerks. Only the movement is much more discernible in quartz watches. In spring watches the movement of the seconds hand is guided by the oscillations of the balance-wheel driven by the hair spring. Since the balance wheel oscillates several times a second, the seconds hand in a spring watch appears to move smoothly as the small jerks are almost non-discernible. On the other hand, in quartz watches, the battery powers a stepping motor that moves the second hand in a single step once every second, which can be quite easily made out and the movement appears jerky.

        Another reason for the illusion is the difference in the amount of angular movement each jerk produces in a second hand. In spring watches it is only  whereas in quartz watches it moves by as much as  in a single step.