This paper and the algorithm published with it [1] describe a technique for plotting contour (level) surfaces of a function of three variables and briefly discuss FORTRAN 77 code implementing the plotting procedure. The author assumes that the function is represented by its values on a rectangular grid drawn in the interior of a rectangular box. The plotting method used is a type of partial masking scheme. The contours are represented by thick opaque bands rather than the more usual choice of narrow solid lines. No masking is used except behind the bands, where a hidden line technique is employed. This produces a semiopaque plot, which, from the examples given in the paper, seems quite a successful representation. It is possible to plot several contours on the same graph. The examples of these given in the paper do not show up very well as they are represented in black and white with thickened lines to represent colors. No doubt they would be visually more pleasing in color.

An effort has been made to make the code portable by isolating the machine- and plotter-dependent parts of the code. The author provides an inefficient portable version of some parts of the code concerned with bit manipulation, which the implementer is expected to replace by efficient machine-dependent code. The plotter-dependent code uses calls to CALCOMP software. This reviewer would have preferred to see the use of an ANSI or ISO standard plotting language here.