I have two of them. The larger 6x24 is great and I can see marks on the blade from contact with the "diamond" edge. And the blade does feel sharper. The measurements seem accurate. On the 4x8 I had to return one because ? the diamond edge was not seated all the way in the ruler's edge so it added about a hair's width. I exchanged it and measured a new one with the saleslady at the store and it seemed OK, but in actual use, cutting my 1/4" seam allowance its the same tiny overage. The diamond edge also slops outward at the bottom. So that's the second one I've gotten. May contact manufacturer because accuracy is the main factor in cutting as we all know.