a)T_eff,r − T_eff,p vs. T_eff,p, where T_eff,r represents the recommended effective temperature. T_eff,p is the best-determined effective temperature from our methodology. Five symbols stand for the five benchmark stars, while two (or three) of the same symbol indicates that spectra obtained with different instruments were analysed. It is the same for the log g_r and log g_p that are shown in panel b).