Abstract: In a process for checking the dimension of a part, the part is moved continuously through a parallel beam of light, in a direction perpendicular to the axis of the beam, and forms a moving shadow on a pair of spaced photoelectric cells. The cells are spaced apart a distance such that there is a zone in the movement of the part in which both cells are partially shadowed and the sum of the areas of the illuminated parts of the surfaces of the cells is measured at the moment when the difference between the areas of the illuminated parts of the surfaces of the cells is zero, and compared with a reference.

Abstract: Apparatus for controlling the position of a part, e.g. a feeler or work tool, along two orthogonal directions, the part being slideable in a first slide extending in one direction and mounted on a carriage movable along a second slide extending in the other direction and mounted on a support. The apparatus comprises a device for locating the position of the carriage on the second slide and the movable part on the first slide, a device for measuring the error in straightness of said second slide and a device for measuring the error in orthogonality of the first slide, each device comprising a laser generator for producing a laser beam parallel to the respective direction and a photoelectric detector in the path of the respective beam and subject to the respective error to be measured.

Abstract: A measuring device includes means for producing an image of a transmitting iffraction grating, means for shifting the image by an amount related to the quantity to be measured, and a receiving diffraction grating for measuring the shift of the image. Each diffraction grating includes a plurality of tracks of increasing pitch, each track of the transmitting grating having a corresponding track on the receiving grating. The device may form a refractometer.