Deviation measures χ_C (upper panel) and χ_Η (lower) against the number of bins for the four stars, computed for the strategy with five fixed λ-separators at λ ∈ (381, 726, 1383, 2636, 5023) nm and with varying number of τ-separators (1, 2, 3, 5, 6, 8, 10, 12, 14, and 16) and therefore varying total number of bins (12, 18, 24, 36, 42, 54, 66, 78, 90, and 102 bins). Solid lines: deviation measures for Q computed using a different number of {τ, λ}-bins. Circles: deviations for Q computed with the Rosseland opacity. Pluses: deviations of the optimal combinations of four τ-bins (see Sect. 5.1 and Table 4).