Special optical, mechanical, and electronic techniques have been combined in a new instrument—the microdeviometer—in which a beam of light and two optical gratings are used to obtain a very accurate scale of distance. The location, with respect to this distance scale, of the salient periodic features in the structure being measured is established through the interception of a second light beam by the structure. Electronic circuitry automatically stores and processes the position information and feeds the processed information, in the form of deviations from the corresponding ideal structure, to a pen recorder. A measuring accuracy of ±1 &mgr; has been consistently obtained, and measurements which formerly required nearly 2 man‐days are accomplished in less than 10 min.