Four examples of nebular line profiles of Hα (red), [N II] 6584 (blue), and [S II] 6731 (green) lines, and their best-fit models using both one- and two-Gaussian models (black, cyan and dark-green dashed lines, for Hα, [N II] and [S II] respectively). The ordinate scale is the same for all lines. Only pure-sky spectra from Giraffe are shown. Each panel labeled with sky position shows the observed spectrum with superimposed the one-Gaussian best-fit model for each line. Below it, the fit residuals (labeled “1-g”) for the one-Gaussian model are shown, with an ordinate scale enlarged 15 times; still below, the fit residuals for the two-Gaussian model (labeled “2-g”) are shown on the same scale.