The factor of proportionality M called the mutual inductance btwn the two circuits Remark M has the unit weber/ampere= henrys M depends on the geometrical configurations of the two circuits, including their sizes, shape, orienta tions, positions M is positive if the flux pr roduced one circuit is related to the current in the other circuit by the ht-hand rule. For instance, Fig. 12-1 gives a pos itive m the directions for the currents are chosen arbitrarily