If you use the cutting lines on the mat, soon you will have permanent grooves and your mat on the measurement lines and it will become useless -- I turn the mat over and don't use any lines at all but use the ruler for measurements. Also make sure each ruler you use are synced. Not all rulers are equal, and if you swap between ruler, make sure each measures the same. Hold them together and check to see if the lines match up - surprise, many don't especially if you have different brands.