Comparison of average observed and best-fit profiles with theoretical NLTE profiles. Bottom panel: spectra from a time series in the QS on disc centre. Top panel: spectra from an AR map off centre. Thick black line: average observed QS profile. Thin purple line: average best-fit QS profile. Blue line: LTE profile of modified HSRA. Red/orange lines: NLTE FAL-C/A profile. For the AR, average profiles of a plage area (blue-dotted line) and an umbra are over-plotted (orange-dash-dotted line). The vertical dotted line denotes the wavelength of intensity normalization.