A freely suspended magnet will align itself with the Earth's magnetic
field (assuming no other fields influencing the magnet). The total field (force
T) is resolved into a horizontal component (force H) and a vertical component
(force Z). We try to keep the magnets in a direct reading compass as close as
possible to the local horizontal by suspending them below the pivot point and,
in some cases, by adding weights to bias them for the northern hemisphere or
the southern hemisphere. The alignment of the horizontal component of the
Earth's field is, therefore, the azimuthal alignment of magnetic North.