Table 1. Approximate sums of squares of deviations between trial surfaces and four-point equations that model them. Column 1 lists typical functions applied to P=(5+x+3y). Columns 2-5 list the sums of squared deviations as rendered by the bilinear-equation model, two quadratic-equation models, Eq. (A) and and Eq. (B), and one cubic-equation model, respectively. The results in the last two columns are derived by the artifice method. See the Discussion