A quantity is said to be exact if it has a precise and well-defined value.
J. W. Tukey remarked in 1962, "Far better an approximate answer to the right question, which is often vague, than the answer to the wrong question,
which can always be made precise" (Bailey et al. 2007, p. 25).
Bailey, D. H.; Borwein, J. M.; Calkin, N. J.; Girgensohn, R.; Luke, D. R.; and Moll, V. H. Experimental
Mathematics in Action. Wellesley, MA: A K Peters, 2007.
