16½in x 16½in square ruler with a unique patented Sharpening EDGE that keeps your rotary blade sharp as you cut.Similar to a knife sharpener, when a cut is made along the sharpener side, the blade runs along the 650 grit diamond carbide EDGE and gets sharpened.. Fully frosted backing provides the perfect amount of steadiness and reduces visual clutter. Large, easy to view numbers and the 3 colour marking system; BLACK Lines mark 1in intervals, RED Lines mark ½in intervals, and WHITE Lines mark ?in intervals. Diagonal line markings have extra large dots for fabric positioning. Designed with extra visual helpers and 30°, 45° and 60° angles.