International audience The neo-classic exercise of growth economic accounting for a given country leads to a quantified diagnosis of the characteristics (capital, work, total productivity of the factors) of this growth while working with a function of Cobb-Douglas production. In the presence of biased technical progress (i.e. progress not profiting identically with all the productive factors), this function is not able to separately provide the value of each bias, which can disorientate the economic policy. In this paper, we provide theoretical and empirical details necessary in economics of technical progress and precisely on the subject of the technical biased progress. We show then exhaustively and pedagogically why the Cobb-Douglas function does not allow a separate identification of these bias and is condemned to gather them within the Solow residual.