Difference between the primary and secondary maxima of the mean magnetic field modulus against the difference between its two minima; both differences are normalised via division by the difference between the primary maximum and primary minimum. Open circles represent stars whose longitudinal field reverses its sign over a rotation period; the dot corresponds to a star with non-reversing longitudinal field. The dashed line is drawn to help the eye visualise the fact that the difference between the minima is generally smaller, and never much greater than the difference between the maxima. The only star above this line is HD 200311, for which no ⟨ B ⟩ data could be obtained between phases 0.6 and 0.9. More observations of the star in this phase range might possibly shift its representative point below the dashed line.