15.64.30.2  Example  - 
     TD:SET GRID DOTS VERT SYM=1O
When  the  axes are plotted, a grid is drawn consisting of vertical dotted
lines at each large X tick, and symbols at the intersection of large X and
Y ticks.
     TD:SET GRID DOTS VERT HORIZ
          is the same as ...
     TD:SET GRID DOTS ON

     TD:SET GRID RED ON PERMANENT
All subsequent plots with axes have red grids.

     TD:SET GRID SYM=0O THETA=90 PHI=90
The  grid will be plotted with crosses as the grid symbol, oriented normal
to the Y axis.  The symbol lies in the XZ plane.

     TD:SET GRID X Y Z YZ ZX DOTS OUTLINE PERM
Plots  grids only on the YZ and ZX planes.  Since only the XY plane exists
for normal plots, TD will only put grids on 3-D plots.