Results of the optimal sub-bin combination search with ten sub-bins. Top panel: best sub-bin distribution for each bin as a function of wavelength for the FALC atmosphere model. For the description of colors confer Fig. 6. Bottom panel: ratio of ODF to detailed spectra showing the single unique sub-bin combination with the lowest cumulative least squares error in all bins (blue), using Kurucz sub-bins (orange). The curve showing best sub-bins for each bin from the upper panel has such a low error that it is indistinguishable from the y-axis.