This chapter discusses technical aspects of the design and operation of plane Fabry–Perot interferometers in the practical modes of operation. In any practical interferometric arrangement the overriding technical aims are the establishment and the maintenance of strict parallelism of the etalon plates throughout the course of the experiment. An additional aspect of the multichannel operation of the photographic method arises because in most cases the source is imaged onto the plane of the fringes. There is thus a one-to-one relationship between a point on the fringe plane and a point in the source or an angular direction to the source. One of the interferometers to employ optical contacting, for use in a solar rocket spectrograph, was described by B. Bates et al. A. Jackson David and R. G. Priest has also outlined the use of a single-board, microcomputer based controller for a Fabry–Perot interferometer.