This is a picture of our prism gauge and the photo is from one of our greens. It helps us measure the actual cutting height of our mowers vs. the bench setting. It is a hand held device that has a mirror placed on an angle to view the grass at the ground level. Our greens mowers are bench set at .125. When we buy new equipment and the cutting unit design has changed we can use this gizmo to make sure the new mowers are the same as the old mowers.