Drop. In horology, when one of the teeth of the contrate wheel reaches the edge of the pallet retaining it, the opposite tooth falls quickly against the other pallet and gives it a slight shock; the shock and the space traversed by the wheel are called the drop . Drop is necessary to avoid the catches that would inevitably result from play in the pivot holes, wear on the parts, and unevenness in the teeth of the contrate wheel. See Catching.

If a little drop is absolutely necessary to an escapement, providing too much is very harmful to a watch or clock. The resulting drawbacks are much less freedom in the vibrations of the regulator, and added wear on its pivots and pivot holes, the tips of the teeth, and the place on the pallets where they strike.

In a well-made escapement, the drop is equal for both pallets; equality is reached by adjustment of the tip of the potence. See Potence tip , Slide , Potence.

Drop is also used in movements for the small arc traversed by the wheel when one tooth leaves the leaf of the pinion and another encounters the next one. Drop becomes considerable in pinions with low numbers, but it is slight when there are eight, ten, or twelve leaves. When a train is too heavy, there is much drop , which causes jumps in the motion of the wheels. See Gears.