I bought them because two sizes are more profitable and give a wider range of use than one. I needed something that would allow me to define an angle of 70-72 degrees to build small pyramids. I'm fascinated by the theories of all the things pyramids are supposed to do, so I wanted something that I could use to create the right angles. An angle of 70-72 degrees should be optimal, plus I've wanted a decent protractor for a long time, plastic just doesn't cut. Well built and sturdy, they warn you not to get your fingers in the way when folding and unfolding. I would recommend them to anyone who wants a durable and useful protractor.