Example of analysis of C IV spectral region of SDSS spectra. The fitted lines are reported as labels. The components employed in the fit are colour-coded, as shown in the legend. The reported C IV outflow velocity is measured as the shift of the outflow component with respect to the BLR component. The dashed vertical lines indicate the expected position for the fitted lines according to the redshift reported in the catalogue. The shaded light grey regions are telluric bands, narrow absorption lines, or bad pixels and are therefore excluded from the fit. See Appendix A for the analysis of other sources.