Patent ID: 7425829

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 portable device for rotating a single, static magnetic field about an axis in a way which produces a rotating magnetic dipole field and for movement in relation to the surface of the ground by an operator; at least initially establishing a known elevational relationship between the portable device and the boring tool; at least periodically sensing said rotating magnetic dipole field, starting in said known elevational relationship and using a receiver that is provided as part of said boring tool to at least periodically produce a receiver output responsive to the rotating dipole field; and monitoring a positional relationship between the boring tool and the portable device by using the receiver output to establish at least a depth of the boring tool such that changing the positional relationship, by moving the portable device nearer to the boring tool, causes an increase in accuracy determination of the depth, as determined using the receiver output.