Patent US 4,023,911

Random dot stereograms are used as stereopsis test targets to align stereomicroscopes in a technique for inspecting three-dimensonal objects. The random dot stereograms are computed and mounted on a holder such that they simulate inspection conditions of the three-dimensional object being inspected. The appearance of a pattern in depth on the random dot stereograms is an objective test as to whether the microscope has been adjusted properly by the inspector. In addition, random dot stereograms can also be used to (1) screen inspectors for stereodeficiencies, (2) facilitate the training of inspectors, and (3) monitor inspection rate control and fatigue of inspectors during inspection.