I bought the Bloc-Loc 6.5" Half Square Triangle ruler years ago and it helps so much with accuracy. The next year, when I visited their vendor booth at a quilt show, I got the Half Rectangle Triangle ruler (actually two rulers in the pack since there is a left and a right), and also got the book that has about 50 quilt block designs using the HRT rulers. I've bookmarked quite a few blocks to try (more than I will probably get to make, lol). Instructions are included for four different size blocks and then each pattern shows two different colorways that give different effects for inspiration. Some of the patterns (i.e. Storm at Sea) combine the half rectangle and half square triangles The rulers are a bit expensive, but worth every penny for the accuracy.