This is fantastic circle-maker from Omnigrid® that has saved my bacon more than once. It's terrific. You slip it onto a wooden yardstick placing the "pointy thing" at one end and the "thing with the lead" (sorry to get so technical) at a mark on the ruler half the size of what you want your circle to be, and bing-bang-boom you get a compass that will make that size circle. Imagine: you could make a 72" circle if you wanted too. For smaller circles, any ruler 1" wide will do. This is a must-have gadget.