Sample Fortran usage
     
   real*8    positions(3,max_ncharge),   radius
   integer   ncharge
c---------------------------------------------------------
c  Set the radius for *all* displayed spheres.
c---------------------------------------------------------
   radius = 0.03d0 
c---------------------------------------------------------
c  Call with ncharge > 0 for normal display.  A graphics 
c  window will be opened interactively the first time 
c  this routine is called in a program (the outline of
c  a small window will appear on the screen; you will have 
c  to position and size the window).
c---------------------------------------------------------
   call sphplot(positions,ncharge,radius)
c---------------------------------------------------------
c  Call with ncharge < 0 (presumably at the end of the 
c  simulation) for "tumbling" display.  Depress the escape 
c  key in the graphics window to return from the routine.
c---------------------------------------------------------
   call sphplot(positions,-ncharge,radius)