Abstract: A method of testing the hardness of a workpiece having a continuously curved outer surface, in particular a pipe or rod, by the penetration method, includes (a) holding the workpiece in a horizontally and vertically fixed position; (b) arranging a machine tool and a hardness testing instrument having a penetration body above the workpiece for movement with respect to the workpiece; (c) linearly scanning a predetermined area of the curved surface of the workpiece for determining the distance between a distance sensor and the curved surface, the region lying in the horizontal path of the machine tool; (d) determining the summit point of the scanned curved surface area from the scanning operation of step (c); (e) selecting the scanned curved area as the test location for the horizontal positioning of the hardness testing instrument; (f) selecting a locus along the scanned curved area of the workpiece as the reference point for the vertical positioning of the machining tool; (g) machining a region into the surfac

Abstract: Two photoelements with inputs for different wave lengths of radiation from a common source are serially connected individually to the inputs of high gain inverting amplifiers with feedback to adjust the voltage across the photoelement to zero, so that the outputs of the amplifiers are proportional to the short circuit currents through the photoelements. An algebraic calculating circuit forms the ratio of the outputs of the amplifier and provides for indication and/or control. The effectiveness of this ratio output is controlled in dependence upon proper orientation to the radiation emitting source.