This easy to use ruler, from Fons & Porter, takes the math out of cutting 1/2 square and 1/4 square triangles. It lets you cut both types of triangles from strips, rather than by cutting squares diagonally into triangles.
This ruler is really wonderful! I was pleasantly surprised with how easy it was to use and how accurate my half square triangles turned out. There are so many different ways to my HST (and quarter square triangles). Using this ruler is another helpful way to cut them, all without having to find that pesky 7/8" measurement on your ruler. Glue Basting my cuts, after using the ruler, made piecing the bias seam of the HSTs simple and prevented stretching.