- for energy storage in the winding (as mainspring, located in the barrel)
- at the balance wheel (balance spring) as part of the oscillating system
- as shock protection
The spring of the balance is also called hairspring (flat spiral). It was invented in 1675 (according to another source in 1665) by Christiaan Huygens. Here the points of attachment of balance staff and balance cock (stud) lie on the same plane.
Although flat spirals have worse results than Breguet hairsprings (see below), because they - unlike those - don't move exactly concentric during expansion and contraction, they are the most common type of spiral in mechanical watches.
Balance springs made of spring steel have the disadvantage that they are changing their elasticity with temperature fluctuations. This also changes the speed of the clock. In the 1930 years, after intensive research, a new balance spring has been developed consisting of an alloy of different metals, which was able to compensate temperature changes. In 1933 these springs entered the watch market under the name "Nivarox". Because of its advantage over normal spring steel, they attained a rapid spread. Today Nivarox is also the name of the most famous manufacturer of flat spirals.
Abraham-Louis Breguet invented this type of balance spring (also called Breguet hairspring), which has a bent terminal curve. Especially Rolex, unlike many other luxury watch manufacturers, is using this type of hairspring in its models. See also the new Rolex development of the Parachrom blue spring.