Additionally, you don't have to "draw" the line. You can press the square in half and use the press mark as a guide or you can use an awesome gadget called "Clearly Perfect Angles"
http://www.newleafstitches.com/shop/...s-x8319256.htm
It is a plastic sheet that sticks to your machine bed and gives you a guide where to sew so you don't have to mark. I have one and love it.