Top panel: part of the intensity spectrum of HD 94660, arbitrarily normalised (black); circular polarisation spectrum V(λ) /I(λ) (red); null (verification) spectrum), shifted vertically by −0.5 for clarity (blue); uncertainties of V/I and null spectra, shifted vertically by −0.5 for clarity (light blue band). The green stripes above and below the spectrum show regions included in ⟨ B_z ⟩ measurement in the H lines; pink stripes show regions included in the metal line measurement. Lower left panels: correlation diagrams for determination of field strength from V/I and I using H lines (upper box) and using metal lines (lower box). Lower right panels: the same with the null spectrum.