Table 1.

Expected compass responses for a torque detector based on magnetic remanence and anisotropic susceptibility, respectively. Realization of a polar compass requires a remanence-based detector that transduces both magnitude and rotational sense of the torque, m × H (equation (2.1a)). Without transducing the sign (i.e. the rotational sense) of the torque, a remanence-based detector produces axial output information only. |m × H|, magnitude of torque and |m × H| = 0, null-detector principle according to Edmonds (1992).

	remanence, m			anisotropic susceptibility χ
	m × H	|m × H|	|m × H| = 0	χH × H
polar compass	+	−	−	−
axial compass	−	+	+	+