A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a resonant device; it swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates.
From its invention in 1656 by Christiaan Huygens until the 1930s, the pendulum clock was the world's most precise timekeeper, accounting for its widespread use. Pendulum clocks must be stationary to operate. Any motion or acceleration will affect the motion of the pendulum, causing inaccuracies. Nowadays, these clocks are kept mostly for their decorative and antique value.
Winding
If a pendulum clock has no winding holes, then it's powered by battery. If the clock has one winding hole, it is for the main time spring. If the clock has two winding holes, the second hole (that's usually on the left) is for the hour and half hour chime. If the clock has three winding holes, the third hole (down at the center) is for the chimes every 15 minutes. The key and the crank are shown at the picture.
Wind up clocks typically have 1-day, 8-day, 14-day or 31-day movements. Small clocks like cuckoo clocks often must be wound daily. Mantle clocks usually have 8-day movements, and larger pendulum clocks may have 14 or 31-day movements. Although clocks may run a few days longer than specified, they should be wound daily, weekly, twice a month or monthly, depending on the type of clock, to assure the most accurate time...
