The Balance Wheel forms part of an assembly which functions to regulate the speed at which the train of wheels turns within a watch movement.
The balance will spin on it’s axis (the balance staff), a certain amount of distance until it is arrested by the tension of the Balance Spring which will cause it to travel an equal distance in the opposite direction.
The diameter and weight of the balance wheel, combined with the length and strength of the balance spring will have a direct influence on the rate of the movement.
It is very important to understand the function of the Balance Wheel within a watch movement and you can learn more about this in our Watch Repair Course Level 1 and Level 2. You can learn how to troubleshoot issues with the balance wheel and further fault finding techniques in level 3
Because the diameter of the balance wheel is critical to the accurate timekeeping of a watch, they will generally be manufactured from a metal alloy named Glucydur which has a lower tendency for expansion than other materials such as copper or iron.
Some balance wheels can be adjusted by the use of timing screws or weights in order to fine tune the rate but the more common method of fine tuning the rate would be to effectively shorten or lengthen the balance spring by use of the regulator arm.« Jargon Buster Index