I had the ruler's 45 degree line on the block diagonal like you said. I started out with 10" squares, but didn't check the size after sewing. I think I was trying to square them up to 9". I didn't use a pattern, so there was no set block size. I know that if you want to do hour glass blocks this way, having the squares 1 1/2" bigger, gives you room to get a nice square block. Perhaps I should try to square it up to 8 1/2".