1. J.C. Maxwell, Treatise on Electricity and Magnetism, Oxford University Press, Oxford, 1873.
2. On the theory of scales of measurement;Stevens;Science,1946
3. R.A. Fisher, The Design of Experiments, Oliver and Boyd, London, 1935.
4. C.E. Shannon, W. Weaver, The Mathematical Theory of Communication, University of Illinois, Illinois, 1949.
5. U. Eco, A Theory of Semiotics, Indiana University Press, Bloomington, 1979.