The basic formula for quantitative elemental measurements by use of core loss signals in EELS has been proposed by Egerton and a rather complete discussion can be found in : Sc (α,Δ) = N.Io (α,Δ).σc(α,Δ) This formula enables to measure the partial cross section for a given edge when applied to standards of known composition and thickness, and the results are to be compared with a priori calculations of the corresponding oscillator strengths in atomic models. With the knowledge of these data, one can then estimate the number of atoms contained within the probed volume, which are responsible of the occurrence of the signal. The above formula constitutes in fact an approximation to take into account multiple scattering events which partially transfer the characteristic signal distribution outside the angular α and energetic Δ parameters of collection.