1. Acton, F. S. Quality Progress, Vol. 1, No. 12, December 1968, p. 8.
2. Acton, F. S. Analysis of Straight-Line Data, John Wiley, New York, 1959, pp. 49–50.
3. Draper, N. R., and Smith, H. Applied Regression Analysis, John Wiley, New York, 1966, Chapter 1, pp. 1–43.