If you own a quartz watch, you’ll know that every couple of years, you’ll need to change the battery. With a mechanical watch, there is no battery.
Instead, every mechanical watch, whether self- or manual-winding (the former using the movement of your wrist to “wind itself”, while the latter is winded by the turning of its crown), needs a barrel in which a wound-up mainspring that stores potential energy is contained.
The mainspring is a long coil of metal that’s been flattened into a ribbon and heated so that it has a memory. When it is wound up tight, the movement’s power is at its fullest. Conversely, a mainspring that is completely unwound means that the movement no longer has any power. It is usually between 20 and 30cm long, and movements can have anything from one to four mainspring barrels.
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The barrel is equipped with teeth around the edges so that it can be geared to the winding mechanism. Every turn of the crown or swivel of the rotor winds the barrel. At the same time, the barrel is connected to the going train of the movement. Energy travels constantly from the barrel through the going train until it reaches the oscillator, which comprises of the escapement, balance wheel, and balance spring.
A watch like the Franck Muller Giga Tourbillon generously exposes the movement’s twin barrels arranged in series. That is to say, energy flows from one barrel into the other before passing through the going train. This is the optimal arrangement to obtain a long power reserve. The Giga Tourbillon, for instance, keeps going for nine uninterrupted days.
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