XQ-100 spectra of the same QSO, J1126−0124, taken with the faulty ADCs in April 2012 (top panel) and repeated with the disabled ADCs in February 2014 (middle panel). Both observations were executed at a similar airmass of ≈ 1.3 at the parallactic angle. The dashed lines indicate the boundaries of the X-shooter arms. The match is better between the VIS and NIR arms in the middle panel. The bottom panel shows the same February 2014 XQ-100 spectrum but smoothed and rebinned to SDSS resolution (blue line), and rescaled by a factor of 1.3 to match the corresponding SDSS spectrum (overlaid in red). The good match suggests that slit losses in the XQ-100 data are roughly achromatic.