Case material: Steel; Charge: Manual; Conditions: New Presentation condition : With boxes and all papers; Model: Tourbograph Price on request Gmtbroker Reference: 712.050 A. Lange & Sohne 712.050 Complete Details: Limited & Numbered Edition Of 50 Pieces Worldwide! Homage To F. A. Lange Tourbograph "Pour Le Mérit". Some characteristics of this watch: The case material used is 18kt "HONEY" colored gold, exclusively developed for Lange & Sohne. The honey gold has a subtle warm hue to it & has a color somewhere between white gold & yellow gold. With a Vickers hardness of over 300, this gold is about twice as hard as other gold alloys , making it more scratch resistant. "Fusee-and-chain transmission": In the Lange & Sohne fusee-and-chain mechanism, the flow of power between the mainspring barrel and the going train is established indirectly by a 636-part chain. One end of the chain is attached to the barrel drum and the other to the fusee. As the mainspring barrel unwinds, the chain wraps around it and reels off the fusee. When the mainspring is fully wound and thus exerts great force, the chain pulls at the smaller radius of the fusee where the leverage is smaller. As the springs tension diminishes, the chain pulls at the larger radius with the higher leverage. Thus, regardless of the state of wind of the mainspring, the same amount of torque is delivered to the escapement, resulting in improved rate accuracy. In the fusee-and-chain transmission mechanism, there is one situation when the cone rota