$ coordinates corresponding to
<CODE>(I,J)</CODE> must be related to <CODE>I</CODE> and
<CODE>J</CODE> by:
$$\eqalign{x = a + b<CODE>I</CODE> + c<CODE>J</CODE>,\cr
           y = d + e<CODE>I</CODE> + f<CODE>J</CODE>.\cr}
$$
The constants $a, b, c, d, e, f$ are supplied to <CODE>PGCONT</CODE> in a six-element
Fortran array.  The other input required is an array containing the
contour values, i.e., the constant values of $f$ corresponding to each 
contour to be drawn. In the following example, we assume that