Comparison of observed T_eff,obs with predicted effective temperatures T_eff,theo for stars in our Milky Way binary sample and its consequence for stellar luminosities (cf. Tables 3 and 4). Panel a) shows a direct comparison of the observed and predicted effective temperatures, panel b) the differences of these temperatures ΔT_eff = T_eff,obs − T_eff,theo as a function of observed effective temperature and panel c) the resulting differences of the observed and predicted bolometric luminosities Δlog L = log L_obs − log L_theo. The squares show stars with fractional main-sequence ages τ/τ_MS younger than 35% (models not influenced by core overshooting) while the filled circles represent τ/τ_MS> 35% (models influenced by core overshooting).