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