Comparison of the derived stellar parameters as a function of S/N. The y-axes show the difference between the value for each parameter derived from the low S/N spectrum and the value derived from the final combined spectrum (i.e. that used in the analysis in Sect. 6. The stellar parameters of the five stars are given in the legend. The colours (indicated in the legend) refer to how many spectra have been combined to obtain the analysed spectrum.