Part of the region of the spectrum of HD 166473 that is common to all the high-resolution spectra from which the mean magnetic field modulus measurements of Table 1 were obtained. Shown are Stokes I (upper panel) and Stokes V (lower panel) spectra, recorded at phases 0.052 (solid red line) and 0.602 (dashed blue line); they are normalised to the local unpolarised continuum intensity I_c. The main lines are Nd IIIλ 6145 Å (not fully resolved), Fe II/Iλ 6147.7 Å (with a quadruplet pattern), and Fe II λ 6149.2 Å (a doublet, blended on the blue side with an unidentified rare-earth line).