This escapement is a variant of the pinwheel escapement. In the usual French pinwheel escapement, the two pallet arms are of unequal length. Jean Andre Lepaute reasoned that the friction and impulse at the pallets must differ, and constructed an escape wheel with two sets of pins. The pallet arms are of equal length, one arm engaging pins on the front of the escape wheel, the other engaging pins on the back. This arrangement made impulse and frictional losses equal on both pallets.