Overview of the FELIS template fit to a simulated spectrum of a C III emitter with a doublet flux ratio of F([C III])/F(C III]) = 1.4 corresponding to an electron density < 10⁴ cm⁻³ (Osterbrock & Ferland 2006). The top panel shows the simulated spectrum (black) with the best-fit scaled template plotted on top (green). The second panel shows the S/N spectrum, that is flux/. The third panel from the top shows the template cross-correlation S/N calculated with Equation A.6. The maximum value is indicated by the vertical dashed red line in all four panels. The bottom panel shows the χ² estimate of the template cross-correlation.