Escapement of most pendulum clocks, and for the development of the grandfather clock, the first anchor clock to be sold commercially, which was invented around 1680 by William Clement, who disputed credit for the escapement with Hooke. The escapement increased the accuracy of pendulum clocks to such a degree that the minute hand was added to the clock face in the late 1600s (before this, clocks had only an hour hand). The anchor consists of an escape wheel with pointed, backward slanted teeth, and an "anchor"-shaped piece pivoted above it which rocks from side to side, linked to the pendulum. The
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