Escapement of clocks, points to the late 13th century as the most likely date for the development of the modern clock escapement. Astronomer Robertus Anglicus wrote in 1271 that clockmakers were trying to invent an escapement, but hadn't been successful yet. On the other hand, most sources agree that mechanical escapement clocks existed by 1300. Actually, the earliest description of an escapement, in Richard of Wallingford's 1327 manuscript "Tractatus Horologii Astronomici" on the clock he built at the Abbey of St. Albans, was not a verge, but a variation called a "strob" escapement. It consisted of a pair of escape wheels
Lever escapement the escape wheel must recoil a small amount during the unlocking. The draw holds the lever against the banking pins during the detached portion of the operating cycle. Draw angle is typically about 11-15 degrees to the radial. Early lever escapements lacked draw (indeed some makers considered it injurious as a cause of extra friction in unlocking); as a result a jolt could result in the escapement unlocking. Most modern mechanical watches are jeweled lever watches, using manmade ruby or sapphire jewels for the high-wear areas of the watch. A cheaper, less accurate version of the lever escapement is used