I love the Magic 8 but I learned it on Lynn Wilder's website, sewn wild oaks, and her formula is to add 1" to the finished size HST and multiply by 2 to get the size of the 2 large squares to start with. It is a great site with lots of pictures. I made Lady of the Lake with 700 + HST and this method was great. After I got done with making all of these, I bought the Blocloc HST template. I highly recommend their templates. I have several HST and Flying Geese templates and they make it so easy.