find a flat level surface with a flat vertical wall at the edge of it. drive up to vertical wall and mark the center of yer lights on the wall.. now drive back abart 15 ft or so and adjust the main beams till they center on yer marks. that works fer me but i do usually have them checked asp afterwards....
last time was when i swapped single lights to dual lights on me jag and that wur spot on according to the machine