There are only very few companies in the world that possess the technology and the know-how to produce balance springs, The Lange & Sohne factory is one of them. The production of top-quality balance springs is one of the most complex processes known in horology. It imposes extremely strict requirements on precision, both in the mechanical shaping operations and in the thermal treatment phases. One example: springs must be rolled to an accuracy of 100 nanometers. This corresponds roughly to one-hundredth of the diameter of a human hair.