This is exactly what the Wonder Cut ruler does. All the markings for cutting both the strips and the HSTs are on the ruler, so there is no math involved. The advantage over Thangles is that you can make up to (I think) a 6" HST this way with no papers to buy.
Originally Posted by Pamela Artman
I just saw a new technique (new to me anyway) that I'm going to try the next time I need HSTs. Cut two strips on the bias, sew down both sides, use a triangle ruler or small square ruler to cut them laying the center line on the seam line and cut first from one sewn edge and then flipping it over and cutting on the other side. I'm thinking the HST won't need trimming to size because you are basically doing that as you cut them from the strip. Sounds easy anyway!