The accuracy of the assumption that LEED spectra for differing inner potentials can be found by shifting calculated spectra along the energy axis is studied. The spread in angle of refraction in typical conditions up to angle of incidence θ = 25° is shown to be small. The variation of θ with energy that minimizes the spread is found. Statistical analysis of data from three different surface structures shows the assumption to be adequate at least up to θ = 25°. © 1981.