Abstract: Apparatus and method by which an unmanned, trackless, work-producing vehicle is able to follow a path defined by a passive metallic marker or markers or by which the vehicle can receive information represented by passive metallic markers. Metallic markers can be secured or applied to appropriate surfaces, such as the floor surface of a vehicle work area, and do not need to be connected to any signal-generating device.An alternating magnetic field is generated by a master coil carried on the vehicle. The alternating magnetic field produces a secondary field around the metallic marker. Both magnetic fields produce voltages in a plurality of spaced secondary coils located on the vehicle. The existence of the metallic marker as a bench mark is identified by comparing the phases of voltages produced by the primary and secondary fields in each separate secondary coil. This excludes any stray fields, which may be extraneously produced in the secondary coils.