When working with fabrics there are bound to be little imperfections. By squaring up each unit as you complete it, you can ensure that the finished blocks will be perfect when sewn together to allow your quilt top to lie flat. Use the vertical, horizontal, and diagonal lines to square up any 16 inch pieced, appliqued or embroidered block. The Ruler has 4 cutting edges, all with 1/4 inch seam allowances for a perfect finished 16 inch block. Ruler has clear 1 inch and 1/2 inch markings for accurate measuring. The Ruler is made of heavy gauge acrylic and is laser precise.