I'm making blocks for a block swap and they require eight half-square triangles (1/2 sq tri). Rather than do them two at a time by cutting 3 7/8" squares, I figured out how to make eight at a time. This is not something new, many others have demonstrated this technique. I just wanted to write my own instructions to refer to.
First, you need to know what size 1/2 sq tri you will be using. My block calls for a 3" square finished. Add 7/8" to that measurement equalling 3 7/8". Now multiply that by two, equalling 7 3/4".
I cut a 7 3/4" square from my light and one from my dark. On the wrong side of the light with a pencil, mark a vertical and horizontal line at the center. Then mark both diagonal lines.
Stitch 1/4" on both sides of the diagonal lines. Cut on all the drawn lines, taking care not to move the pieces until all lines are cut.
Press seam to the dark side and you have eight half-square triangles!