Reliability of the correction spectrum investigated by comparing the composite spectrum of DR7 and BOSS spectra. While the black line shows the composite spectrum from DR7 spectra at the faint epoch, the red and blue lines are composite spectra at the faint epoch for uncorrected and corrected BOSS spectra, respectively. All three composite spectra were normalized at 2250 Å. The good match between blue and black spectra strongly favors the reliability of the correction spectrum. The upper small panel shows the number of objects in each wavelength bin (1 Å) when constructing the corresponding composite spectra.