Abstract: An apparatus for measuring a dimension of a workpiece, for instance a worece being machined on a lathe, comprises a unit which may be moved toward and away from the workpiece. That unit includes a forked carriage one of the prongs of the fork having a light source which directs a parallel light beam perpendicularly to the direction of movement of the carriage toward the other prong. Light sensitive means on the other prong deliver a first signal when the light beam is interrupted by the workpiece upon movement of the unit and a second signal when the light beam is re-established.

Abstract: A machine for measuring the dimensions of a workpiece, comprising a base te for receiving the workpiece and a mechanical structure carrying a feeler for movement along three orthogonal axes at right angles by means providing for direct measuring of the amounts of movement of the feeler along the axes. Optical deviation measurement means determine the errors due to deformation of the components, lost motion as well as pitch, yaw and/or roll of the movable components. The corrections to be applied to the data delivered by the measuring means are computed and may be made automatically for the display to be free of errors.