THE FUSÉE-AND-CHAIN TRANSMISSION.

When fully wound, the mainsprings of mechanical watches deliver more torque than when they are nearly unwound, and this can cause rate inaccuracies. The fusée-and-chain transmission is perhaps most elegant way to eliminate this phenomenon. But it is so difficult to craft that only Lange's master watchmakers have had the courage to integrate it in the confines of a wristwatch.

Driven by the spring barrel around which it winds itself, the 636-part chain transmits its pulling power to the going train as it unwinds from the fusée, a stepped cone. When the mainspring is fully wound and thus exerts the most force, the chain pulls at the smaller circum-ference of the cone - according to the principle of levers at the shorter lever. When the tension of the mainspring is nearly depleted, the chain pulls at the larger circumference of the cone, at the longer lever. The result is uniform power transmission regardless of the state of wind of the mainspring. This improves the rate accuracy of the watch.

THE STEPPED PLANETARY GEAR.

In the fusée-and-chain transmission mechanism, there is one situation when the cone rotates backwards: as the mainspring is being wound. To prevent the watch from stopping while it is being wound, Lange's master watchmakers integrated a marvel of miniaturisation inside the fusée. It is a tiny planetary gear train that assures uninterrupted delivery of power to the movement.