With no arguments GRID produces a simple axes. The addition of x1 and y1 cause a grid to be drawn. The x1,y1 values specify the spacing between grid lines.
A value of zero (the default) disables grid lines in that direction. Grid lines are drawn across the entire soft-clip area. The values x2,y2 specify the origin of the grid; the defaults are 0,0.
The values of x3,y3 substitute short tick marks in the place of full grid lines. A value of n specifies that only 1 out of n divisions use a full grid line. The other (n-1) divisions use tick marks instead. The defaults are 1,1. This disables tick marks because full grid lines are drawn for all the divisions.
The minor value specifies the size of tick marks. The default is 2 graphic display units.
