Same as Fig. B.1, but for a FEROS observation of the star NGC 6611-001. This is an example of a model fit to a double-lined binary (SB2) system, thus treating the object as a single star. The grey-shaded boxes guide the eye to recognise the binarity signatures in the most pronounced cases, i.e., the contributions of the two stars to the asymmetric line profiles. The neglect of the binary nature (see also Sana et al. 2009; Lefèvre et al. 2009) results in the analysis yielding incorrect atmospheric parameters and elemental abundances. Some deficits in the modelling, such as for the O ii features around 4070 Å, stem from missing lines in the spectrum synthesis (see Fig. B.1).