The Ronchi Ruling pattern (also called a diffraction grating) consists of equally spaced alternating clear and opaque bars. The spatial frequency of the ruling is typically expressed in Line Pairs per MM or Line Pairs per Inch.
The pattern is printed in Chromium (OD > 3.0) on 1.5mm thick Soda Lime Glass and extends to the edge of the glass. The transmission tolerance for the 120 LPMM pattern is ±7.5%.
A complete drawing is available under Detailed Specifications below.