↑ Ernest Nagel: "Measurement", Erkenntnis, Volume 2, Number 1 / December, 1931, pp. 313-335, published by Springer, the Netherlands
↑ Stevens, S.S. On the theory of scales and measurement 1946. Science. 103, 677-680.
↑ Douglas Hubbard: "How to Measure Anything", Wiley (2007), p. 21
1 2 3 Baber, Zaheer (1996). The Science of Empire: Scientific Knowledge, Civilization, and Colonial Rule in India. State University of New York Press. p. 23. ISBN 0-7914-2919-9.
