Abstract: An alidade surveying instrument, comprising a pair of gimbeled yokes, a mounting base supporting the pair of gimbeled yokes for rotation on axes perpendicular to one another, a ranging device carried by the gimbeled yoke pair for targeting a remote object both as to elevation and azimuth, a first gear set coupled to one of the yokes and second gear set coupled to the other yoke, a pivot plate supporting one of the gears of each gear set for a varying degree of gear meshing with respect to its associated gear, and a spring for applying a variable force to the pivot plate for driving the gears of each gear set into a yielding engagement to counteract physical variations in the degree of gear set engagement as the gears of each set mesh and rotate relative to one another.