15.64.65.4  LEVEL   - INSIDE,OUSIDE,  or  LEVEL=n  sets  the window level.
Levels may range from 1 to 4.  INSIDE increases the level by 1 and OUTSIDE
decreases  the level by 1.  Using this option you may inset windows inside
other windows.  When you increase the LEVEL by 1  the  current  window  is
used  to set the maximum limits of the new window.  You may increase LEVEL
by 1 or decrease it to any number from 1 to the current level.   When  you
increase  the  level,  you have effectively decreased the plot size to the
current window size.

                                  example
As  an  example  you wish to create a set of six windows within a definite
location.
     TD:SET WINDOW X FROM 1 TO 12 Y FROM 1 TO 7
Set the outer level
     TD:SET WINDOW 1 OF 6 INSIDE
          or...
     TD:SET WINDOW 1 OF 6 LEVEL=2
Now  you  have 6 equal size windows bounded by 1,1 and 12,7.  To return to
having only 1 window
     TD:SET WINDOW LEVEL=1
                                  example
     TD:SET WINDOW X FROM 1 TO 12 Y FROM 5 TO 7
     TD:SET WINDOW LEVEL=2 FROM 1,1 TO 2,2
Insets  a  window within another.  The actual physical location of the new
window is X=2 to X=3 and Y=6 to Y=7.