Source: Systems Engineering Tools, (1965), p. 108; As cited in: Alberto Ortiz (1992) Systems engineering concept demonstration, process model http://www.dtic.mil/dtic/tr/fulltext/u2/a265469.pdf. p. 12
“A model may be pictorial, descriptive, qualitative, or generally approximate in nature, or it may be mathematical and quantitative in nature and reasonably precise.”
Source: Systems Engineering Tools, (1965), p. 108
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Harold Chestnut 27
American engineer 1917–2001Related quotes
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Source: Systems Engineering Tools, (1965), p. 108; As cited in: Alberto Ortiz (1992, p. 13)

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as quoted by Ilya Prigogine in his Autobiography http://nobelprize.org/nobel_prizes/chemistry/laureates/1977/prigogine-autobio.html given at the occasion of Prigogine's 1977 Nobel Prize in Chemistry.