Measured EW (bottom) and velocity (top) as a function of the S/N for the perturbed SN 2002an spectra shown in Fig. C.4 (black) and also for perturbed spectra of SN 2013K (purple), SN 20l3ai (green), and SN 2007oc (red). The points are the mean of ten different simulations for a given S/N, and its associated error bars are the standard deviations (SN 2007oc has too large errors on the velocities and are thus not shown). The dashed error bars of the EW are the mean of the errors calculated from the automated technique. Upper right ticks show the S/N of the original unperturbed spectra.