void fgrid (lnstyle, ndiv) GRIDOPTS.C Level 1
char lnstyle  = 0 for no grid lines or subdivisions (default).
 = -1 for tick marks only.
 = 19 selects the line style used for the grid lines (see below)
int ndiv The number of desired subdivisions between main grid lines on the axes. The major tick marks are not included, so to have 10 intervals, set ndiv = 9.
fgrid() allows you to draw one or more grid lines between adjacent axis tick marks. This feature can be used to create fine grid divisions without causing the axis labels to overlap. With logarithmic axes, the requested number of divisions is ignored, and the number of grid lines depends on the logarithmic base of the axis. fgrid() also allows you to put small tick marks at subdivision spaces without drawing grid lines.

Available line styles: