Watch GlossaryBalance Wheel
The balance wheel and the hairspring constitute the regulating organ of a watch, which is responsible for maintaining the precision of a mechanical watch
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What is a balance wheel in a watch?
A balance wheel (also known as balance), is a device, which is an integral part of mechanical watches. It is defined as a ‘weighted wheel that rotates back and forth, being returned towards its centre position by a spiral torsion spring, (better known as the balance spring or hairspring).’ It is driven by the escapement, which ensures that the rotating motion of the gear train is converted to impulses that are delivered to the balance wheel. So, one can say that the balance wheel and the hairspring inside it together form the regulating organ of a watch. Together, they oscillate preferentially at a certain rate, forming a resonant frequency or ‘beat’, which also prevents it from oscillating at other rates.
To simplify the terminology, the balance wheel rotates around the axis of the wheel in an alternating clockwise and anticlockwise motion, which is controlled by the coiling and uncoiling of the hairspring. Each swing of the balance wheel advances the gear train, which subsequently moves the watch hands. Even the precision of a watch is dependent on the construction of the balance wheel—which usually beats at a frequency of 21,600 or 28,800 ‘vibrations per hour’ or vph in modern watches.
