UVB and VIS sensitivity functions and the resulting flux-calibrated spectrum for GD71. The top panel shows the order-by-order sensitivity functions in AB magnitudes for both the UVB (solid black line) and VIS (dashed red line) arm. The temporal variation of the instrumental throughput at the transition regime of the UVB/VIS dichroic is illustrated in the inset, where we show three different sets of sensitivity functions, obtained on three different nights in the relevant wavelength range. There, the solid green curve indicates our reference set (obtained on 2010 February 10), the dotted black line the set obtained 24 h later, and the dot-dashed red curve depicts the sensitivity functions one week later. The middle panel shows the final flux-calibrated output for GD71 (solid black line), where all echelle orders of both instrumental arms have been merged into one spectrum. The underlying model SED is overplotted in red. The propagated observational 1σ uncertainties are indicated with a smoothed, symmetrical gray band around the mean values and are hardly visible for most of the spectral range. The bandpass selection used as input for the count integration is indicated in green at the bottom of the panel. Atmospheric absorption bands have not been corrected for. The ratio between model and data is shown in the bottom panel. Systematic deviations are typically ≲0.5%, except for wavelength ranges covered by stellar features, where they can increase to ≲4%. We note that the flux-calibrated spectrum of GD71 is plotted with a very high resolution and so the electronic version of this plot is highly zoomable.