The polynomial of degree \(n\) is written \(f_n = g_{k-1} + p_k h_{n-k}\) where \(g\) passes through the \(k\) absolute points \((a,b)\), \(p\) is \(\prod(x - a)\), and \(h\) is to satisfy a least-squares condition. \(g\) is determined by applying the algorithm of \textit{G. E. Forsythe} [J. Soc. Ind. Appl. Math. 5, 74--88 (1957; Zbl 0083.35503)] to the absolute points, and \(h\) by then applying it again to values \((y-g)/p\) calculated from the approximate points \((x,y)\).