The diagram below shows the typical gear train of a watch. The escapement of a watch begins with the escape wheel. Next you will have the pallet. The pallet makes contact with the balance wheel as shown in the diagram. The balance wheel swings back and forth and with each swing locks and unlocks the pallet as it engages the escape wheel. This arc-of-motion can range from 18,000 beats per hour to as much as 28,000 beats per hour on some wrist watches.