Use of Diffraction Gratings for Controlling a Ruling Engine

The general properties of interference moiré fringes arising in the transmission of a light beam through a system consisting of a reflection and a transmission diffraction grating are considered. The method of measuring linear displacements, based upon this phenomenon, is applied to a ruling engine for controlling the motion of a diffraction grating while it is being cut. These engines have been used to rule diffraction gratings of very high quality in all respects.