The dead-beat escapement is attributed to George Graham and was introduced c. 1730. This escapement gives excellent results over long periods when fitted to well-made clocks. The locking faces form arcs of a circle centered on the axis of the pallet staff. The impulsing is similar in action to the anchor escapement, but between impulses the escape wheel remains stationary, locked on the faces on the pallet. This escapement is admirably suited to weight-driven longcase regulators. For spring-driven clocks, the half dead-beat escapement is more suited. In this escapement, the locking faces are formed to give an amount of recoil judged by the maker to counteract any changes in motive power which must occur in a spring-driven clock, as the resistance offered by the recoil counteracts the increase in pendulum arc which occurs when more motive power is available, and vice versa. Towards the end of the 18th century Benjamin Vulliamy introduced a variant of the dead-beat escapement in which the angle between the arms of the pallets is adjustable by a screw.