Ionisation equilibrium of the benchmark star HD 122563. The top and bottom panels display [Fe/H] and v_mic determination under LTE and NLTE respectively. The crosses and circles indicate neutral and ionised species, respectively. Linear regressions corresponding to each species are displayed by different line styles (see legends for, where the values in brackets are the errors of the coefficients). The red line represents the regression of the neutral and ionised species together, the shade is the 1σ standard deviation. Determined [Fe/H] and v_mic values are given in the plots.