Ensure that your quilt tops lie flat every time, carefully square up your blocks before sewing them together! By squaring up each unit as you complete it, your finished blocks will fit together perfectly. Use the vertical, horizontal, and diagonal lines to square up any 12-1/2in pieced, appliqued or embroidered block. The Ruler has 4 cutting edges, all with -1/4in seam allowances for a perfect finished 12in block. Ruler has clear 1in and 1/2in markings for accurate measuring.