Poor man's rubber band compass

Recently I had to cut an methacrylate circle of a certain diameter and I had no compass or similar tool to draw the circle. Looked here for a design that meet my needs but couldn't find any. I like simple and functional things and I remembered some tool my drawing teacher used when I was a child... that came to my mind. Not a joke!! This works for me better than any toy. My hands handle this well, not like some toys that always break in my hands. I needed something that I could attach several ki