Verge escapement St. Albans, was not a verge, but a variation called a 'strob' escapement. It consisted of a pair of escape wheels on the same axle, with alternating radial teeth. The verge rod was suspended between them, with a short crosspiece that rotated first in one direction and then the other as the staggered teeth pushed past. Although no other example is known, it is possible that this design preceded the more usual verge in clocks. For the first two hundred years or so of the mechanical clock's existence, the verge, with foliot or balance wheel, was the only escapement used
Anchor escapement it unwinds. An escapement in which changes in drive force do not affect the rate is called isochronous. The superior performance of the deadbeat over the recoil is due to improved isochronism. This is due to the different ways changes in drive force affect the swing of the pendulum in the two escapements: When the deadbeat was invented, clockmakers initially believed it had inferior isochronism to the anchor, because of the greater effect of changes in force on the pendulum's amplitude. Recent analyses point out that the nonisochronism of the anchor can cancel the circular error of the pendulum. That