Hexbin plot of the resulting pseudo-χ² statistic according to Eq. (6) (upper panel) and Eq. (7) (lower panel) for the theoretical model #10001 with a Rayleigh limit of d⁻¹. The colours of the bins show the minimal value of all models that fall within the bin. Black lines show the same evolutionary tracks as in Fig. 1. The correct position of model #10001 is marked with the green circle and the assumed spectroscopic error box is drawn in green.