Abstract: The inspection system detects defects in regular patterns wherein the elements of the patterns may have variations in period. The system includes means for scanning and detecting the elements of a pattern to produce an original output signal indicative of the pattern. Means then delay the output signal from the scanning and detecting means to produce a delayed output signal. Next, any deviation in period between the original output signal and the delayed output signal is detected by suitable means. Means now match the periods of the original and delayed output signals, and other means correlate the matched original and delayed output signals.