Computed values of non-seismic constraints against the observed ones, symbolised by a box, for the system seen as a whole (i.e. with common ages and initial compositions). Each variation in input physics is represented by a different symbol. The colour represents the star, blue for 16 Cyg A and red for 16 Cyg B. The upper panel is a HR diagram. The lower panel shows the surface helium abundance versus the metallicity.