The problem with HSTs made the way toverly mentioned is all of the bias cuts to deal with even on smaller HSTs. If you used this method with really large squares it would really be difficult to manage all that bias. I think it would be better to use the method whereby you draw a diagonal line through your square and stitch 1/4 inch on either side of the line. Press carefully with the seam going to the dark side and then square up. You have much less bias to deal with this way. If you are going to use bigger squares you can use lines on your cutting mat.