Abstract: A method of measuring linewidth loss during the formation of microelectronic circuitry, including the formation of a test pattern constituted by a series of spaced bars on a photographic mask which is to be used to form a predetermined pattern on a substrate material. Either of the bars or the gaps between the bars have the same predetermined width. In the former case the gaps, and in the latter case the bars, have widths which differ incremently stepwise from one to the next. The series of bars are such that the ratio of the widths of one adjacent bar/gap pair is unity.The resultant pattern which is formed on the substrate as a complement of the test pattern is then inspected, and the position where the bar/gap width ratio of the resultant pattern is unity is noted. The linewidth can then be calculated loss from a knowledge of the size of the incremental step and the position of the bar/gap width ratio unity point on the resultant pattern.