Median of the relative error in effective temperature for bins of spectral type found by the FOSC, in a spectral class vs. luminosity class diagram. The colours of the symbols correspond to different runs. As indicated at the bottom, the size and shape of the symbols give the median value of computed over the sample of stars that are classified in the spectral type (i.e. a combination of a spectral class and a luminosity class) of the corresponding abscissa and ordinate. The synthetic magnitudes reproduce the characteristics of the Obscat catalogue.