Logarithm of the effective temperature corresponding to the spectral class found by the FOSC as a function of the model effective temperature. Each symbol corresponds to a simulated star and their colour depends on the quality index QI (see Eq. (3)) as indicated by the colour scale on the right-hand side of the plot. The solid black line indicates the exact correlation and the dotted black lines shows the ± 5% band. The thin horizontal grey lines indicate the effective temperatures of the templates available in the Pickles library. Top: for the sample of “dwarfs” stars classified with luminosity classes IV and V. Bottom: for the sample of “giant” stars, luminosity classes I, II, and III.