1. Process for the approximate calculation of the exponential mean of a string of numbers u.sub.n coded in a floating-point format used to convey certain bit rate information in ATM networks, each number representing bit rate information contained in the RM cells of an ATM network and being defined with the aid of an exponent e.sub.n and a mantissa m.sub.n by a relation of the form u.sub.n =2.sup.e n.(1+m.sub.n /512), characterized in that it consists in approximating the exponential mean by the code value associated with the exponential mean of the code words U.sub.n =512.e.sub.n +m.sub.n.