Abstract: An optical measuring light path formed by a vacuum-side laser beam (Pa) as a reference standard and an optical measuring light path formed by a gas-side laser beam (Pb) as a dimension to be measured are coaxially located sandwiching a movable end (optical transparent body 12) of a vacuum container (11) in order to satisfy Abbe's principle requiring linear disposition of the reference standard and the dimension to be measured in measurement direction, thereby reducing measurement error in measuring air refractive index and improving measurement accuracy therefor.

Abstract: An optical measuring light path formed by a vacuum-side laser beam (Pa) as a reference standard and an optical measuring light path formed by a gas-side laser beam (Pb) as a dimension to be measured are coaxially located sandwiching a movable end (optical transparent body 12) of a vacuum container (11) in order to satisfy Abbe's principle requiring linear disposition of the reference standard and the dimension to be measured in measurement direction, thereby reducing measurement error in measuring air refractive index and improving measurement accuracy therefor.

Abstract: There is provided a length measuring machine which is not influenced by fluctuations of air or changes in temperature. At a structure, graduations are formed in a longitudinal direction, and further a built-in light wave interferometer is provided. The built-in light wave interferometer measures a length of the structure and supplies the data to a current controller. In order to reconcile a length of the structure with a nominal value, the current controller supplies current to an electrical resistor provided at the structure to cause thermal expansion of the structure, or the structure is cooled.

Abstract: A measurement-datum similar to profile of a measuring object set in a measuring area in which a detector and the measuring object are moved relatively is formed to measure the displacement value between the detector and the measuring object through the relative movement based on the measurement-datum to thereby compute the surface contour of the measuring object from the measured data with reference to the measurement-datum. Since the measurement-datum is set in the spatial area, a precise mechanical processing will not be required for an accurate measurement of the measuring object having a strange profile which was not measured by conventional apparatus.

Abstract: An edge detector in an optical measuring instrument, for detecting a transmitted light or reflected light to directly or indirectly measure dimensions of an object being measured, comprising:a sensor including four light receiving elements provided on a plane substantially in parallel with a plane of relative movement between the sensor and said object being measured, whereby at least two sets of phase shift signals are generated in accordance with brightness and darkness generated during said relative movement; a first and a second operational means for calculating differences between the sets of said phase shift signals; a third operational means for calculating a difference between output signals emitted from said first and second operational means and a fourth operational means for calculating a sum of said output signals; and a detecting means for emitting a crossing signal when an output signal from said third operational means is on a reference level, and when an output signal from said fourth operatio