Sky subtraction sequence for GD71. The top panel shows a rectified spectrum of GD71 with an additional sky component. The break point distribution that forms the basis for the fits to the sky spectrum is shown in the second panel, while the corresponding sky model, based on two separate spline fits at either side of the stellar PSF and an additional interpolation along the cross-dispersed direction, is shown in the third panel. The final sky-subtracted spectrum of GD71 is presented in the fourth panel. For comparison, the fifth panel shows the corresponding result obtained with the X-shooter pipeline, which failed to produce an acceptable solution for the shown wavelength range (7742 Å to 7770 Å) and other parts of the spectrum. The color scaling of the sky model is illustrated in the bar at the bottom.