I agree with Joyce888 and others. If it calls for a block size of 3 and 7/8 to make a 3 and 1/2 square I cut the square at 4 in. it gives me just enough to square it up. I, too, am a pencil down the center sewer of half square triangles. Squaring them up is key to a perfect quilt. I also use the idea of sewing on the back to see where the seams are.