I've always used the lines on the mat - and that is why I DON'T like the Olfa mats - the ones with every 5th inch line thicker than the others. Also, I have a ruler on which the first quarter inch is at least 1/16th too wide. So, I use the Fiskars mats, with Gingher rulers, try to hold the rotary straight up and down, and find everything works out great.