Abstract: A method and apparatus provides a three dimensional measurement of a point on an object. A surface with a system for detecting the position of sensors is placed adjacent to the surface and an assembly disposed adjacent to the surface yet freely movable within a plane is parallel to the surface. The assembly includes two sensors whose orthogonal projections into the surfce are detected by the two dimensional detecting system. The assembly further includes a probe, slidable only in a direction perpendicular to the surface and a system for detecting the perpendicular distance of the probe from the surface. In this manner, the orthogonal projection of the probe into the plane is permanently fixed in relation to the two sensors. In practicing the method of the invention, the object to be measured is placed adjacent to the surface and the assembly is moved to a position where the contact on the probe can be moved orthogonally until it contacts the spot on the object whose position is to be measured.