Pendulum

• Time in a cuckoo clock is kept by the swinging movement of a pendulum. Generally, a second is ticked for every back-and-forth movement of the clock's pendulum. According to Merritt's Antiques Inc., the weight at the bottom to the pendulum "makes no difference, nor does the distance of the arc: only the length of the shaft matters to how long it takes for a pendulum to swing through an arc." With the understanding the pendulum's speed will never deviate through its arc, clock makers could translate the time it takes a pendulum to go back and forth into second, hours and minutes on a clock.
  
  

Weights and Gears

• Weights wound around the cuckoo clock's internal gears power the clock's movement. The gravitational pull of the weights descending from the clock causes the gears to turn, while the constant back-and-forth motion of the pendulum regulates the descent of the weights. The teeth on the "escapement" gears, according to Merritt's Antiques Inc., "are angled in such a way to provide a precise release and a slight push to the pendulum." Furthermore, the iconic "tick" and "tock" sounds associated with all pendulum clocks is generated from the escapement gear's anchor engaging the pendulum and the sound of the next tooth on the escapement gear falling into place.
  
  

Cuckoo

• The characteristic "cuckoo" sound is created by two bellows and whistles inside of the cuckoo clock. The bellows are top heavy, with flexible, air-tight sides. When bellows are lifted by wires attached to the clock's gears, they are filled with air. When tension on the wire is relieved, the heavy tops of the bellows fall back into place--causing the air inside them to rush out and into the clock's whistles. The two whistles are tuned to the notes of a cuckoo's call--one whistle for the "cu" and the second for the "ckoo" sound.
  
  The cuckoo bird itself is mounted on a hinged bracket. Like the clock's bellows, the cuckoo is controlled by wires attached to the clock's gear mechanism. The application and relaxation of tension on the wires attached to both the cuckoo and the cuckoo's door allow the bird to spring forth, and recede in and out of the door.