Rule 9.4.1:  "The bridge must have a designated straight nominal centerline extending from one end to the other. The centerline must be designated by two holes, one at each end of the bridge, drilled vertically through horizontal steel surfaces at the level of the decking support surfaces. Each hole must be approximately ¼ inch in diameter and must be located no more than 3’0” from the vertical plane defined by the ends of the decking support surfaces."

Common Error:  Teams fail to provide the hole in the right place and/or the right size.  While not stated in the rules explicitly, it is very helpful to the judges if they can pass the centerline measuring string through the hole!