The angle of dip (positive down from the horizontal) of the magnetic lines of force. This varies with geographical position and through time. Along with magnetic declination, this defines the orientation of the Earth’s magnetic field at any given location.
Borehole image and dipmeter tools need to be oriented in space. Orientation is completed by measuring the Earth’s magnetic field (of known orientation) using three mutually perpendicular magnetometers to record the Earth’s magnetic field relative to the tool axis. Tool orientation is then calculated.
See also magnetic declination and magnetic north.