Graduating by Simple Moving Averages and by the Mid-Ordinates of Third-Degree Parabolas Fitted by the Method of Least Squares

Frederick R. Macaulay, The Smoothing of Time Series (NBER, 1931), chap. 2, https://www.nber.org/books-and-chapters/smoothing-time-series/graduating-simple-moving-averages-and-mid-ordinates-third-degree-parabolas-fitted-method-least.