I agree with WinterSewer and Prism. If you plan to make many half square triangles, I strongly suggest you invest in an EASY ANGLE ruler, and if you don't already have a June Tailor Shape Cut I strongly recommend purchasing that, too. Not a day goes by that I don't use mine. You can quickly and accurately cut squares, strips and square up HST and even completed blocks. My Shape Cut in my sewing rooms and my coffee pot in my kitchen are two must haves that I can't live without!