Based on simple physical arguments, the proposed analytical expression: describes the evolution as a function of the incident angle a, of the Auger backscattering factor r (= 1 + R) and of the ionization function of EPMA at the surface, ~(0). This expression leads to a new procedure of quantification in AES and EPMA by the measurement of the electron backscattering coefficient ~ via the measurement of electric current of the correctly polarized specimen holder, which allows the local determination of r and ~(0) without the knowledge of the substrate composition. Its field of application concerns point analysis and images acquisition in Auger electron spectroscopy and X-ray emission spectroscopy with a special attention for the in-depth profiling by AES and the non destructive profilometry of coatings by EDS-EPMA. The results deduced from the proposed expres- sion are in excellent agreement (at least for Uo ~ 3) with the numerical values deduced from Monte Carlo simulations and from the solutions of the transport equation as proposed by other authors. Some aspects related to the influence of the roughness of the surface on the measurements are also indicated.