How The Tourbillon Works

Gravity was thought to have a very adverse effect on the accuracy of time pieces at the time of the invention of the tourbillon, particularly because pocketwatches were often less accurate than stationary clocks of the same construction. The prevailing theory amongst horologists of the time was that pocket watches suffered from the effects of gravity since they were usually carried in the same pocketed position for most of the day, which was vertical, and then held in a different position while being read. Because the movements of pocket watches and similar pieces were oriented with respect to the cases and the dials, their movements were positioned with the axes of motion perpendicular to their faces. This meant that when the timepiece was placed vertically, the axis of motion of the movements would be parallel to the ground, and thus to the force of gravity. In such a position, the force of gravity would affect the motion of parts of the movement differently when the parts were in different positions (i.e., moving with gravity or moving against it), which would cause variations in the rate of the movement, which in turn would affect the timepieces' accuracy. If adjusted for one position, the rate would change when the piece was kept in a different position, such as when being held to be read or when placed on a table at night. In a tourbillon, the entire escapement assembly rotates, including the balance wheel, the escape wheel, the hairspring, and the pallet fork, in order to average out the effect of gravity in the different positions. The rate of rotation varies per design but has generally become standardized at one rotation per minute. Most tourbillons use standard swiss lever escapements, but some have a detent escapement, and others contain novel designs, such as the Audemars Piguet Millenary for example.

The tourbillon is considered to be one of the most challenging of watch mechanisms to make (although technically not a complication itself) and is valued for its engineering and design principles. The first production tourbillon mechanism was produced by Breguet for Napoleon in one of his carriage clocks (travel clocks of the time were of considerable weight, typically weighing almost 200 pounds).