XYGraph__PlotDatum (ul_pbar_graphics)

 *  Synopsis:
 *    #include <ul_pbar_graphics:xygraph.h>
 *
 *    TXYGraph__Result XYGraph__PlotDatum( TXYGraph__Data xData,
 *					   TXYGraph__Data yData,
 *					   int color )
 *
 *  Function intent:
 *    XYGraph__PlotDatum() plots a single data point with a specified display
 *    color.
 *  Function parameters:
 *    TXYGraph__Data	xData		X coordinate
 *    TXYGraph__Data	yData		Y coordinate
 *    int		color		Color of data point
 *  Function return value:
 *    CBS_OK		success
 *    CBS_NOSETUP	XYGraph__DisplayGraph() not yet called
 *    else 		wn_xxx() function error occured