a method and apparatus that will locate the center of a circle in a single operation by positioning two points of registration at the edge of the circle relative to a third point of registration previously set at the edge of the circle where these points are held in accurate spatial relationship to each other and a fourth point of registration that in turn , indicates the center of the circle . by allowing precise registration and novel operation , this invention provides a simpler , more accurate means to locate the center of a circle that precludes the need to make extraneous marks on the circle being measured .