Abstract: Apparatus for measuring the road wheel hub alignment of a vehicle on its production line includes a pair of electro-optical units for attachment to a pair of road wheel hubs and a master control and display unit. The electro-optical units each comprise an array of photo-sensitive devices which are illuminated by a directional beam of light from the other unit, and include a display for indicating to an operator the state of alignment of the hub to which the unit is attached. Alignment of both hubs can be monitored by a display on the master control unit, which includes an output to a data recording means so that the state of alignment of the hubs on each vehicle passing down the line can be automatically recorded. The photo-sensitive devices are arranged in a radial plane of the axis about which the hubs swivel for adjustment, and in a plane perpendicular to the axis of rotation of the road wheels to enable simultaneous independent adjustment of the hubs.