1. International Vocabulary of Metrology (VIM), third ed., BIPM JCGM 200:2012, http://www.bipm.org/en/publications/guides/vim.html December 2022.
2. D. H. Krantz, et al, Foundations of Measurement, Academic Press, NYC, NY, 1971.
3. D. J. Hand, Measurement Theory and Practice, Arnold, London England, 2004, page 27. [2] is considered to be the "magnum opus" on representational theory.
4. P. A. M. Dirac, The Principles of Quantum Mechanics, fourth edition, Oxford University Press, London, 1958, page 18.
5. L. Euler, Elements of Algebra, Chapter I, Article I, #3. Third edition, Longman, Hurst, Rees, Orme and Co., London England, 1822. Original work published in German in 1765.