The one crucial piece of information that I had somehow missed for squaring up for a long time was that you have to use the diagonal line on your ruler and make sure that it is exactly on the diagonal of your block and then trim around. For a long time I couldn't figure out why my half square triangles were not evenly split in half by colour as I had used the proper sized square for trimming. However I had just plopped the square down, hacked off the excess and had not been checking the diagonal. It makes a huge difference. Now how did I miss that? I finally understood when I saw a demonstration on squaring up at our guild meeting the night we offered Tips and Tricks.