The traditional mean value function f .1 ((1/n)./(xi )) is known to be determined by a certain set of basic axioms (Kolmogoroff 1930; Nagumo 1930).It is argued here that one of these axioms is meaningless in the case of only two arguments.Thus it is not very reasonable in the case of two arguments to restrict attention to the familiar mean value function.This argumentation is illustrated with reference to the problem of calculating growth rates.A family of growth rates is introduced where all common procedures of calculating growth rates are included as special cases.