Combined mean spectrum (black) and rms spectrum (red) of WPVS 48 from our campaign. The partition in the two intercalibrations (see Sect. 2 for details) is shown with a grey dashed line. The rms spectrum was scaled to allow for a direct comparison. The analysed continuum regions and the identical pseudo-continua used for linear continuum subtraction are highlighted with blue bars below the spectra. The line integration limits are marked by the shaded areas. All emission lines of He I are displayed in orange.