An example (IW Car) of an SED of a post-AGB star with negligible pulsational variability. Left panel: measured photometry (circles), which are filled if the data were used in the fitting process. The colour indicates the photometric system, as listed in the legend. The full black line is the best-fit SED model that abides the spectroscopic temperature constraint (see the red cross in the middle and right panels). The exact parameter values of this model are given in the figure. The dashed black line is the same model, but unreddened. A consistent vertical scale, and colour coding for the photometric systems, is used for all stars in the sample (see Appendix B). Middle panel: confidence interval of the angular diameter θ_⋆ vs. the effective temperature T_eff. The dashed red line corresponds to the spectroscopically measured effective temperature. The dotted red lines indicate the 3σ lower and upper limit on this temperature. Right panel: confidence interval of the reddening E(B−V) vs. the effective temperature T_eff.