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...http://www.google.es/patents/US5421096?utm_source=gb-gplus-sharePatente US5421096 - Gear driven alidade assembly
