Patent ID: 7570060

Claim:
In a system including a boring tool that is movable underground using a drill string which extends from the boring tool to a drill rig that operates at the surface of the ground, a method comprising: configuring a transmitter for above ground use and for rotating at least two static magnetic fields that are produced by a first magnet and a second magnet rotating about a first axis and a second, different axis, respectively, in a way which produces a first rotating magnetic dipole field and a second rotating magnetic dipole field such that the first and second rotating dipole fields are distinguishable, one from the other; using a receiver that is provided as part of said boring tool, at least periodically sensing said first and second rotating magnetic dipole fields, to produce a receiver output responsive thereto; and monitoring a positional relationship between the transmitter and the boring tool by using at least the receiver output to establish an actual position of an overhead point that is directly above the receiver in a laterally spaced-apart relationship from the transmitter.