US Patent 7856729 Bore elevation and azimuth measuring apparatus and method

A method for measuring the azimuth and elevation of the axis of a tube of other apparatus uses a centering mandrel inserted in the tube. The centering mandrel has a laser fixed to one end. The laser beam is aligned with the bore axis of the tube. A pair of optical instruments view two points on the laser beam. Using the optical instruments, horizontal and vertical angles from one optical instrument to the other, and vice versa, are measured. Also, horizontal and vertical angles from each optical instrument to each of the two points are measured. Using the three sets of measured angles, the azimuth and the elevation of the bore axis are calculated.