Escapement may avoid the need for lubrication in the escapement (though it does not obviate the requirement for lubrication of other parts of the gear train). The accuracy of a mechanical clock is dependent on the accuracy of the timing device. If this is a pendulum, then the period of swing of the pendulum determines the accuracy. If the pendulum rod is made of metal it will expand and contract with heat, shortening or lengthening the pendulum; this changes the time taken for a swing. Special alloys are used in expensive pendulum-based clocks to minimize this distortion. The degrees of arc
Grasshopper escapement in the stable block at Brocklesby Park in Lincolnshire. This proved to be unreliable, needing repeated attention by which Harrison was inconvenienced, so around 1722 he modified the escapement by putting a hinge in the middle of each arm of the anchor. The hinged pallets both pointed the same way, opposing the rotation of the escape wheel. As the escape wheel pushes the pallet, the hinge moves away from the escape wheel. The pallet pivots about its contact point with the wheel as it pushes the anchor. At the same time, the other pallet is approaching the wheel. When it