David H. Krantz; R. Duncan Luce; Patrick Suppes; Amos Tversky (1971). Foundations of Measurement: Additive and Polynomial Representations. I. Academic Press. pp. 10–11. ISBN0-12-425401-2
R. Duncan Luce; David H. Krantz; Patrick Suppes; Amos Tversky (2007) [1990]. Foundations of Measurement: Representation, Axiomatization, and Invariance. III. Dover. p. 112. ISBN0-486-45316-2