And I start by measuring the square to make sure it really is 10x10. Then, instead of cutting 2 1/2 inches 3 times, being right handed, I measure from the left and make my first cut at 7 1/2 inches and then the next at 5 inches and finally a 2 1/2 inch cut. If there is a tad of discrepancy, it is spread across all the cuts more evenly. I try to keep the piece nice and straight, turn my cutting mat 90 degrees and repeat the process.