Anchor escapement position is isochronous for different drive forces, ignoring friction, and that the deadbeat escapement approximately satisfies this condition. It would be exactly satisfied if the escape wheel teeth were made to fall exactly on the corner between the two pallet faces, but for the escapement to operate reliably the teeth must be made to fall above the corner, on the 'dead' face. A major cause of error in clocks is changes in the drive force applied to the escapement, caused by small changes in the friction of the gears or the pallets, or the diminishing force of the mainspring as
Anchor escapement is still a frictional rest escapement because the sliding of the escape tooth on the dead face adds friction to the pendulum's swing, but it has less friction than the recoil escapement because there is no recoil force. In contrast to the backward slant of the anchor escape wheel teeth, the deadbeat escape wheel teeth are radial or slant forward to ensure that the tooth makes contact with the 'dead' face of the pallet, preventing recoil. In 1826 British astronomer George Airy proved that a pendulum that is driven by a drive impulse that is symmetrical about its bottom equilibrium