Abstract: A method and system to determine the relationship between a laser plane and an external coordinate system using a mobile machine with a work implement is provided. The laser plane is intersected at three points by a laser receiver installed on a mast attached to the work implement. A position determining antenna located a known distance on the mast from the laser receiver is used to determine external coordinates at the position determining antenna point. An equation for the laser plane in external coordinate terms is determined based on the three external position coordinates and the known distance between the external coordinate system plane and the laser plane.