Veritas Router Circle-Cutting Center

It is easy to cut and edge profile circular table tops or similar discs using a router. You just take a 4" or 5" wide strip of thin plywood or hard board, fix one end to the base of your router, measure the radius you need along the strip and then what? The dilemma has always been how to securely anchor the strip at the circle center without having to drill a hole in the work.