I was sorting through my rulers and found this one. I don't remember using it so I thought I'd try it out. Wow. This is wonderful for HSTs. I put two 2 1/2" squares together, put the ruler on it made one cut. I had a perfect 2 1/2" Hst and one 2" hst. No lines to draw, no 7/8" added. Works to add corner to square to make square in a square perfectly. It's simple and inexpensive compared to a lot of the other speciality rulers. I'm keeping this little jewel out of the drawer.
