I use my set-in triangles ruler all the time for diagonal set quilts. Mine is by Lynn Graves at Little Foot, Ltd. It is was made by Omnigrid. With the measurements on it, all you need is the size of the unfinished blook to be able to cut the setting triangles from a strip of fabric and not have to cut a big square and cut it in 4-corner to corner. Gets rid of a whole bunch of math and formula.