Reference X-Shooter NIR-arm model transmission spectrum binned in 1 nm steps for a mean amount of precipitable water vapour (PWV) of 3.1 mm and an airmass of 1. The bins marked by red symbols are classified as continuum. The transmission of these bins ranges from 0.95 to 1.00. The mean value is 0.99. The selected bins are used to derive the systematic offsets (residuals) in the telluric absorption corrected spectra. Bins that belong to four specific transmission ranges corresponding to T = 0.9 (blue), 0.8 (cyan), 0.5 (magenta), and 0.2 (green) are indicated as well. The figure also shows the fitting ranges (yellow bars) that were used by molecfit (see also Table 4).