Observed average of the mean quadratic magnetic field against the observed average of the mean magnetic field modulus. Open symbols are used to distinguish those stars for which either or both of ⟨ B_q ⟩ _av and ⟨ B ⟩ _av were computed using less than 7 individual measurements of ⟨ B_q ⟩ and ⟨ B ⟩, respectively. The short-dashed line corresponds to ⟨ B_q ⟩ _av = ⟨ B ⟩ _av. The long-dashed line represents the least-squares fit of the observed relation between ⟨ B_q ⟩ _av and ⟨ B ⟩ _av; it is based only on the stars for which at least 7 measurements of both ⟨ B_q ⟩ and ⟨ B ⟩ are available.