A calibration-test member in the form of a ball plate fixedly mounts a plurality of precision balls arrayed in spaced relation in a single plane. The ball plate is of symmetrical construction with respect to this plane, the balls being so mounted within one or more cutouts of the plate or on the edge...http://www.google.es/patents/US4962591?utm_source=gb-gplus-sharePatente US4962591 - Calibration-test member for a coordinate-measuring instrument
Calibration-test member for a coordinate-measuring instrument
