This 3-1/2" square ruler was designed by Marsha McCloskey to measure from the center. Make extremely accurate 4-triangle squares by first cutting the triangles larger than they need to be, then stitching the triangles to make a square. Center the Precision Trimmer 3 on the sewn unit and trim the edges to the perfect size.
I also use the Precision Trimmer 3 as a point trimmer. Here are 2 ways to use the ruler to trim the 3/8" points from triangles.