We have developed theoretically a generalized least squared fitting, using as fitting function the exponential of a cubic polynomial, and as data, the efficiency ratios between different wavelengths in the vacuum ultraviolet spectral margin. The fitting function is suggested by the linear interpolation of efficiency ratios whose wavelengths are nearby. We have tested the fitting proposed for data offered by different authors in literature, obtaining a determination coefficient above 98%.

Keywords: Vacuum Ultraviolet, Line Ratios, Generalized Least Squared Fitting