This is a tool for alining a Cab interior to a loco a.cabfront or a.cabback. To use place on track and add a fixed camera alining with the two bars. Drive loco up to aline with the two bars at the Cab side window. You can then see if the Cab View (1) matches View (3) all so if you see ether of the two boxes in the Cab the height is wrong, boxes set at 3 ft 5 in and 14 ft 10 in.