Indicators I_off for systematic offsets (upper panel) and I_res for small-scale residuals (lower panel) of the telluric absorption correction for single 1 nm bins of the X-Shooter NIR-arm spectrum shown in Fig. 2. Both quantities are given as a function of transmission. Bins belonging to the different transmission ranges used in the discussion are marked by different colours (see legend and Fig. 1). Small red symbols identify bins which are excluded from further analysis due to either very low transmission or very weak line strength.