I use the disk...Triangulations (computer disk). It has hundreds of sizes of triangles, flying geese and other things (I don't have the disk in front of me).
What you do is find out what the finished square/triangle needs to be. You find the page on the disk, print out the pages you need, then sew directly onto the pages. Each and every page you make more than 1 hst square.
When you do it you take 2 pieces of rectangular fabric (face/face), lay the paper on top of this, sew on the lines they tell you to, then cut where it tells you to. You will end up with perfect triangles each and every time.