Average apparent bolometric magnitude as a function of ν_max (left panel) and Δν_cor (right panel) for our sample of RGB (red and green dots) and RC (blue dots) stars in NGC 6791 and NGC 6819, respectively. The dotted lines in the left panel (and top inset in the right panel) correspond to BaSTI isochrones (Z = 0.03 and 8.0 Gyr for NGC 6791 and Z = 0.02 and 2.5 Gyr for NGC 6819) arbitrarily shifted to match the observations. The loops in the isochrones correspond to the various phases of the RGB evolution. Solid lines in the right panel indicate polynomial fits to the RGB stars. The bottom inset gives the mass of the BaSTI isochrones normalised to the mass at ν_max =100 μHz.