  We introduce a methodology to calibrate in situ a set of coils generating bi-
or tri-axial magnetic fields, at frequencies where a calibration performed
under static conditions would be inaccurate. The coil constants are determined
in a two-step procedure. Considering the presence of a static and a
time-dependent field, firstly, the static one is oriented perpendicularly to
the polarization plane of a time-dependent one; secondly, the polarization of
the latter is made accurately circular. The methodology uses harmonic analysis
of one component of the magnetization of an atomic sample whose spins
adiabatically follow the time-dependent field.
