in 1930 and used it as the basis for the company's Oyster Perpetual, in which the centrally mounted semi-circular weight could rotate through a full 360° rather than the about 200° of the 'bumper' winder. Rolex's version also increased the amount of energy stored in the mainspring, allowing it to run autonomously for up to 35 hours. Information about 18th-century rotor watches was not published until 1949. Although the Oyster Perpetual was probably an original invention, the company may have known of Coviot's 1893 patent that re-invented the 18th-century design. Glycine and mass production of automatics With John Harwood's patent for self-winding watches set to expire in the early 1930s, Glycine founder Eugène Meylan started developing his own self-winding mechanism. Meylan’s design was unusual: a separate module that could be used with almost any 8.75 ligne (19.74 millimeter) watch movement. In October 1930, Glycine released their first automatic watches using this module, which became the world's first widely-produced automatic watches. This allowed Glycine to survive the global depression in the 1930s that caused many Swiss watchmakers to close shop. Eterna ball bearing The next development for automatic watches came in 1948 from Eterna Watch. To wind a watch effectively, one of the chief requirements of a rotor is heft. Until this point, the best bearing used in any watch was a jewel bearing, which perfectly suits the small gears of a watch. A rotor, on the other hand, requires a different solution. In 1948, Eterna introduced the solution that is still in use today: ball bearings. Ball bearings provide robust support for a heavy object to rotate smoothly and reliably even under abnormal stress, such as if the watch were dropped. Eterna adopted geared bidirectional winding shortly afterwards. Carl F. Bucherer weighted geared ring By the 1960s, automatic winding had become widespread in quality mechanical watches. Because the rotor weight needed in an automatic watch takes up a lot of space in the case, increasing its thickness, some manufacturers of quality watches, such as Patek Philippe, continue to design manually wound watches, which can be as thin as 1.77 millimeters. However, in 2007 Carl F. Bucherer implemented a new approach without a rotor, a peripherally mounted power source, where a geared ring and a rotating unbalance mass segment made of tungsten encircles the entire mechanism, rotating on carbon rollers whenever the watch moves. A system of clutch wheels captures power.