Abstract: A method is based on utilization of interference patterns for determining an increment of a third coordinate with two given coordinates. An interference pattern is produced on a surface under investigation whereupon one of interference bands is marked to obtain a zero reference band. The subsequent step is to determine the attitude of an interference extremum surface corresponding to said reference band. Thereafter the period of all extremums is distributed along the axis of the third coordinate and an increment of the third coordinate is determined relative to the surface of the zero band by adding up values of periods of surfaces corresponding to bands between the zero reference point and two predetermined reference points.A device for accomplishing the hereinproposed method comprises an optical system for producing an interference pattern, a photorecorder to record said pattern, a coordinate setting unit, and a unit for determining the number of the band of the recorded interference pattern.