Reduced χ² between the synthetic and observed spectra for the cores of the 12 strongest lines for the star GJ 176 as a function of the observed flux in the centre of the lines (filled symbols). The symbols are the same as in Fig. 2 and refer to the parameters used for the synthetic spectra. The upper panel shows the whole range of χ² while the lower panel focuses on χ² below 50. The open symbols indicate the χ² of K lines generated in non-LTE for L2016 or L2017 and P2019. The identifications of all lines are presented in Table 5 together with the wavelengths and observed fluxes.