void erfgrid (ymin, ystep, ymax, yformat) ERFPLT.C Level 2
float ymin The minimum data value for the y axis.
float ystep The change in y between tick marks on the y axis.
float ymax The maximum data value for the y axis.
char *yformat The y axis format string.
The routine erfgrid() draws the axes and grid lines that appear on ERF or percent paper. The x axis of an ERF plot 
is scaled on cumulative percentage. The y axis is scaled linearly. Thus, the user has control over the y axis scaling only. Results for a normal (Gaussian) distribution (a bell-shaped curve) are expected to be a straight line on the ERF grid. The arguments for this routine are similar to the y axis parameters of the graf() routine.