Deviation measures χ_C (upper panel) and χ_Η (lower) versus the number of bins, for the four stars (colours as in Fig. 1), for the case of {τ, λ)-binning approach similar to Magic (2014). Solid lines: deviation measures for the Q computed using 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, and 100 bins distributed as in Fig. 13. Circles: deviations for Q computed with the Rosseland opacity. Crosses: deviations for Q computed with only two τ-separators located at the heights of the bins in the UV (no λ-separators). Pluses: the deviation of the optimal combinations of four τ-bins (see Sect. 5.1 and Table 4).