cal output is produced and output to a molecular graphics plot file.
       The original version of HOLE directly produced a HYDRA/QUANTA binary
       3D plot (.qpt) file.  This contained a dot surface showing the locus of the surface
       of the moving sphere and a line showing the locus for the sphere centre. 
       <!--Also available is an option which draws a line from the two atoms closest
       to each sphere surface to that surface.  This is intended to be useful in
       analyzing which atoms 