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A balance wheel, or balance, is the timekeeping device used in mechanical watches and small clocks, analogous to the pendulum in a pendulum clock.It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral torsion spring, known as the balance spring or hairspring.
In watch movements the wheels and other moving parts are mounted between two plates, which are held a small distance apart with pillars to make a rigid framework for the movement. One of these plates, the front plate just behind the face, is always circular, or the same shape and dimensions as the movement.
A typical fully jeweled time-only watch has 17 jewels: two cap jewels, two pivot jewels and an impulse jewel for the balance wheel, two pivot jewels and two pallet jewels for the pallet fork, and two pivot jewels each for the escape, fourth, third, and center wheels. In modern quartz watches, the timekeeper is a quartz crystal in an electronic ...
Button, coin, or watch cells. A button cell, watch battery, or coin battery is a small battery made of a single electrochemical cell and shaped as a squat cylinder typically 5 to 25 mm (0.197 to 0.984 in) in diameter and 1 to 6 mm (0.039 to 0.236 in) high – resembling a button.
Center or second wheel which turns once per hour. Its pinion is turned by the teeth on the mainspring barrel in watches and spring driven clocks, and by the weight pulley in weight driven clocks. Its arbor projects through a hole in the face and drives, via a friction coupling, the cannon pinion , which carries the minute hand .
These watches were called jerking watches because, even with buffers, when the weight hit the case the whole watch would jerk. Center-weight The weight pivots in the center of the movement and rotates clockwise and anti-clockwise. The weight is supported by a bridge that blocks the rotation and it is limited to about 180°. [15]
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Verge timepieces tend to accelerate as the crown wheel and the pallets wear down. This is particularly evident in verge watches from the mid-18th century onward. It is not in the least unusual for these watches, when run today, to gain many hours per day, or to simply spin as if there were no balance present.