The orientations of borehole image and dipmeter tools need to be referenced to north. The azimuth at any time of pad 1 acts as this reference in relation with magnetic north. It is given in degrees (more rarely in radians) referenced clockwise from north. It is not defined for a well section that is horizontal. For holes deviated up to approximately 30º the relationship RB = P1AZ – hole azimuth should hold.
RIDER, M., 1996. The Geological Interpretation of Well Logs, Whittles Publishing, Caithness, p280.