Synthetic spectra of only hydrogen lines (black) and duplicate transitions (green) synthesised for five BRASS benchmark stars: HR 7512 (B8 III), 68 Tau (A2 IV–Vs), Procyon (F5 IV–V), 51 Peg (G2.5 IV), and Arcturus (K1.2 III). Most duplicate lines produce a maximum depth, for the given spectral parameters, of less than 1% of the continuum in this work. A small number of Fe duplicates produce maximum depths, at cooler stellar parameters, of at most 10% ofthe continuum.