Inside the watch

If you don’t happen to have the previous issue of beyond to hand, here’s a summary of our first topic: the mainspring lies coiled up inside the barrel. By turning the winding crown or setting the oscillating weight in motion, we activate the barrel arbor, which winds the mainspring. The mainspring tightens and wants nothing more than to return to its original state, but is prevented from doing so. The result is tension, or energy, which is stored there in the mainspring barrel and released in a carefully controlled manner. 

Which brings us to the going train, whose job it is to transform this raw spring force into a steady flow of time. Put simply, it works like this: as the mainspring unwinds, the barrel rotates slowly but with considerable force, its gear teeth meshing with the first wheel in the going train. This wheel already rotates a little faster and transfers the motion to the next wheel. This sets in motion a chain of gears, pinions and transmissions that are calculated to ensure that, at the end of the sequence – where, for example, a hand is attached – they achieve the correct rotation speed to display the time. 

This gear train consists of at least three main wheels: the centre wheel, the third wheel and the second wheel. Let’s take a common, simple movement, such as the ETA 6497 (see right). Here, the centre wheel is the minute wheel: the shaft in the centre runs through the entire movement; the minute hand sits on top of it. The teeth of the centre wheel mesh with those of the third wheel. This serves solely to transmit the energy to the second wheel in the most efficient way possible. The seconds hand, after all, needs to rotate at a much higher speed than the minute hand. The more dials and complications our watch has, the more gears it needs. They are all connected to the same power source, but each converts the energy individually into the required rotational speed. 

So what happens within the going train between the mainspring barrel and the escapement is a marvel of geometry: the movement of bodies through space, time, velocity and acceleration. It is not just the size of the wheels that plays a role, but also the shape of their teeth – and that of the space between them. We’ll spare you the mathematical equations: we can’t assume that all our readers are as nerdy as we watchmakers are. I