Patent ID: 8076940

Claim:
A method to determine a fixation point of a rod in a well, comprising: while no torque is applied to the rod about a longitudinal axis of the rod, measuring the magnetic flux due to the Earth's magnetic field that passes through a window attached to the rod; while applying a torque to the rod about the axis, measuring the magnetic flux due to the Earth's magnetic field that passes through the window when attached to the rod at a first location and measuring the magnetic flux due to the Earth's magnetic field that passes through the window when attached to the rod at a second location, wherein the first and second locations are known with respect to a point of origin on the rod; and, determining the fixation point of the rod relative to the point of origin as a function of the measurement of magnetic flux taken when no torque is applied to the rod and a difference between the measurements of the magnetic flux taken at the first and second locations.