The problem of providing sufficient power to drive the escapement with the very high gear ratios necessary to make a clock go for a whole year has been successfully overcome by only a few makers. The wheel work must be proportioned with due regard to its work in the train; the faster-moving wheels (and particularly the escapement) must be made very light so that inertial losses will be minimal; and tooth profiles and pivots must be designed to reduce frictional losses to a minimum. Weight-driven year clocks may be arranged by providing two extra wheels and pinions between the great wheel and the centre pinion, which gives an additional ratio of 52 to 1 over that found in eight-day clocks. Spring-driven year clocks are usually found to contain a number of standard mainsprings, connected end to end, driving the great wheel; though a magnificent year clock driven by single springs and fusees was made by Thomas Tompion for King William III, between 1695 and 1700. The gear frictional losses are reduced by this layout, at the cost of a large number of turns being necessary to wind the clock annually.