The bilinear equation, Eq. (1), has traditionally been used to represent four
numbers in a rectangular array. The array can be represented by the vertices of
face ABDC of the prism in Fig. 1. As its name implies, the bilinear equation is
exact on bilinear numbers. A quadratic equation for the same design is exact
on bilinear numbers and their squares [1]. This paper introduces another
method that renders quadratic equations for the four-point rectangular design.
The two equations can be identical but often they are different.