If the over cut is occuring at the bottom of the cut (as it is in our example) you’ll need to readjust the guide rail stop on the scale by the degree of the over cut to get rid of it. Whatever readjustments (recalibrations) you make now will always be required for the unique marriage of this particular V-Groove Cutter with this particular mat cutter. In other words, if you have to offset by 1/16″ narrower on the top stop to get a perfect corner, you will always have to offset by that amount to get a perfect corner, regardless of the mat.