After identifying Prot and obtaining σP rot , either through a period search analysis or from the literature, final 1 st and 2 nd order sinusoidal fits to each star's Bz (t) and Hp(t) measurements were derived (2 nd order fits were only derived for those **data** sets consisting of more than 5 **data** points). The epoch of each star was defined such that Bz (t0) = |C0 + C1| (i.e. the maximum, unsigned longitudinal field strength) while φ1 and φ2 were constrained such that C1 > 0 and C2 > 0. Note that the way in which the epoch is defined and the way in which C1 and C2 are constrained implies that, for the fits to Bz , φ1 = ±π/2 while φ2 is a free parameter; for the fits to Hp, both φ1 and φ2 are unrestricted free parameters.