Abstract. It is well known that if P t denotes a set of power means then the mapping R ∋ t → P t (v) ∈ (min v, max v) is both 1-1 and onto for any non-constant sequence v = (v 1 , . . . , v n ) of positive numbers. Shortly: the family of power means is a scale.If I is an interval and f : I → R is a continuous, strictly monotone) is a natural generalization of power means, so called quasi-arithmetic mean generated by f .A famous folk theorem says that the only homogeneous, quasi-arithmetic means are power means. We prove that, upon replacing the homogeneity requirement by an invariant-type axiom, one gets a family of quasi-arithmetic means building up a scale, too.