BAlance Spring
Balance Spring - Assembly with engraved balance bridge, Vincent & Scales
The balance spring and the balance spring assembly is the regulating unit controlling the accuracy of the watch.
The unit consists of a flywheel (or balance wheel) with a balance staff, a hairspring (balance spring) fixed to the balance staff and to the regulator on top of the balance staff. The balance staff is suspended by the shock-absorber to protect the balance from induced forces from the use of the watch. The balance bridge is holding the assembly together in the movement.
The balance spring or the hairspring with its square cross-section is normally made of an alloy based on iron, nickel, and chromium however other materials such as silicone based spring materials are used too. The balance spring is a crucial part of the watch functioning. The delivered couple must be unchanged independent of variations in temperature or magnetic fields to keep the accuracy in the time measuring.
In 1920 the Nobel Prize for Physics was awarded to Charles Edouard Guillaume a Swiss physicist for his discovery of the Elinvar an elastically invariable material i.e a material which elasticity remains unchanged in temperature variations.