Comparison between the radii obtained by different combinations of the available observational constraints. Radii are determined using asteroseismic constraints (ν_max,Δν) and T_eff (black dots); determined with PARAM (blue crosses); and using the parallax from the Hipparcos catalogue (van Leeuwen 2007), apparent magnitudes, and extinction from different prescriptions (red symbols). Squares represent radii computed with no extinction (A_V = 0), and triangles extinctions from the 3D Galactic extinction model by Drimmel et al. (2003). Asterisks indicate stars that are members of NGC 6633.