Biproportional methods project a matrixAto give it the column and row sums of another matrix; the result isR A S, whereRandSare diagonal matrices. AsRandSare not identified, one must normalize them, even after computing, that is,ex post. This article starts from the idea developed in de Mesnard (2002) - any normalization amounts to put constraints on Lagrange multipliers, even when it is based on an economic reasoning, - to show that it is impossible to analytically derive the normalized solution at optimum. Convergence must be proved when normalization is applied at each step on the path to equilibrium. To summarize, normalization is impossibleex ante, what removes the possibility of having a certain control on it. It is also indicated that negativity is not a problem.