Average ratios of observed standard star spectrum (corrected for atmospheric extinction) and shifted reference spectrum for UVB and VIS data for the regions containing Balmer lines, using the bump-corrected model spectra. The curves have been normalized at the red end of the respective plot windows, which show the Balmer lines Hα (right), Hβ (middle), and Hγ to H9 (left). The two narrow windows on the right share the same range along the y-axis.