I gave my wonky 6 x 24" (more like 5.712 x 23.863") Olipfa ruler to a non-quilting buddy that needed a straight edge only ruler. She only uses the lines on her cutting mat to measure with. I didn't know about rulers being wrong either until I tried making swap blocks and not only were they not the right size but they weren't even square! Now, I only have Omnigrid rulers and I checked all of them against a Stanley tape measure for accuracy.