Bob,
See photo of a car you should be familiar with ERA 2002. The tech is setting up heads on each wheel . . . turn plates are under each wheel for four-wheel alignment.
The alignment machine shown is an older system using cables to each head that projects a light beam from the heads to a receiver. Newer machines such as those from Hunter use "targets" that reflect light projected from laser beams onto the targets and bounced back from each wheel to a receiver. Once "compensated" by rotating the wheels, lowering the vehicle, then rolling it out, each wheel is read individually for camber and toe. Steering is turned right and left, then centered to get a caster readings. Sure beats the old caster gauge, strings, level and chalk marks on the floor.
