A reliability index ([Formula: see text]) proposed for low-energy electron diffraction (LEED) crystallography by Zanazzi and Jona has been investigated by assessing its ability to compare experimental intensity versus energy curves with those calculated for different non-structural parameters. Included in the latter are the energy dependence of the real part of the inner potential for Cu(111), and the individual variations of the imaginary potential and the surface Debye temperature for Rh(111). Also an error has been corrected in one atomic potential used in our earlier work on Rh(100) and Rh(111), and this allows a resolution of the discrepancy found previously in the geometrical structures indicated by a band structure potential and a superposition potential for rhodium. The results here provide general support for the use of the index [Formula: see text]in conjunction with procedures frequently followed in LEED crystallography.