A. Lange & Söhne caliber L072.1
With a fusée-and-chain transmission and a one-minute tourbillon, the L072.1 as found in the Richard Lange Tourbillon “Pour le Mérite” incorporates two of the most effective complications that increase rate accuracy. Its third complication is the patented stop-seconds mechanism. Thanks to this device, the tourbillon – and with it the entire movement – can be stopped and restarted to one-second accuracy.
Apertures in the three-quarter plate expose the fusée-and-chain transmission, which is so complex that it is rarely implemented in wristwatches. The owner can observe how the intricate 636-part chain unwinds from the mainspring barrel onto the fusée while the watch is being wound. The fusée-and-chain transmission is one of the most effective complications when it comes to increasing the rate accuracy of a mechanical watch. It is one of the tenets of physics that the power generated by a spring is high when it is fully tensioned and significantly weaker as it nears the fully unwound state. This can cause rate-accuracy fluctuations. The fusée-and-chain transmission works like an infinitely variable gearbox. It equalises the waning force of the gradually relaxing mainspring and makes sure that the movement always receives a constant amount of energy.