SHOW /OVERLAY

        [DISPLAY\]SHOW Argument [First [Last]] /OVERLAY [Variable [Channel]]
     [/DIRECTORY NameTree] [/SIDE]

    Overlay  (in  contours)  the specified Channel of the SIC 2 or 3-D Variable.
    The default Variable is CONTINUUM, the continuum image. If Variable is a 3-D
    SIC Variable, Channel indicates which plane is overlaid (default: last one).
    The /OVERLAY option de-activates the contouring of  the  Argument  data,  by
    temporarily setting DO_CONTOUR to NO.

    In  addition  to  this  overlay, the user can add any display on the channel
    maps by a command to be executed through  the  OVERLAY_COM  variable.   This
    command can be the execution of a script, e.g.
              LET OVERLAY_COM "@ draw_my_markers"
    or
              LET OVERLAY_COM "@ p_beam clean"
    to plot the clean beam.

    Note that this variable is not defined by default, so must be defined
              DEFINE Char*80 OVERLAY_COM /GLOBAL
    when needed