New rulers that sharpen your blades

These rulers have one diamond pwd. edge that sharpens the cutting blade in your rotary cutter when used. Tip I read with this sharpening is to also turn your blace around to also sharpen the other side of blade. I ordered a 12 1/2" square, 6 1/2" square, 4 1/2" square and a 6' x 24" ruler. ( Now why didn't I think of this)