the present invention generally relates to a method and system for determining the position and alignment of a plane in relation to an intersecting axis and using that known position and alignment to allow for corrections to be made when using the plane as a reference plane . more particularly , the invention relates to a method and system for determining the angle of tilt of a planar surface in relation to a laser beam , and using the determined angle of tilt to calculate a correction factor to be applied to the laser beam . briefly stated , the method and system ultimately calculates a correction factor , z - offset , that is applied when using the laser beam in a procedure .