Teresa Down under has a video on a square in a square on U-tube. She merely puts the square down on another piece of fabric that is laying right side up, and cuts out another one the same size, making a 'X' across the block, sews it all around the four sides, and carefully clipping on the 'X' mark to open up the square within a square. No math needed. I have shown it to others who wanted to try it. Seems simple enough on the few I made.