Scatter plots of the percentage of channels with intensity in the range [continuum−noise,continuum + noise] against the discrepancy between the determined continuum level and the real one (in percentage). The different panels correspond to the different methods described in Sect. 2.1, as in Fig. 4. In each panel, green dots correspond to synthetic spectra for which the continuum level has a discrepancy <1%, red dots are those spectra with discrepancies in the range 1–5%, blue dots are those spectra with discrepancies 5–10%, and gray dots have discrepancies >10%. The success rate (or percentage of spectra with a given discrepancy) are indicated next to the vertical, colored lines (see also Table 2).