Variables:

            SHOW Image  control variables

    The following variables control the SHOW display.
      Display the header     DO_HEADER   [ YES ]
      Display a color wedge  DO_WEDGE    [ YES ]
      Plot bitmaps           DO_BIT      [ YES ]
      Add the clean beam     DO_NICE     [ NO ]
      Add the UV coverage    DO_COVERAGE [ NO ]
      Add the dirty beam     DO_DIRTY    [ NO ]
      Display the labels     DO_LABEL    [ YES ]
      Display contour levels DO_CONTOUR  [ YES ]
      grey-scale contours    DO_GREY     [ NO ]
      Better marks           DO_MASK     [ NO ]           (Hide image behind cha

      Channel range          RANGE       [ 0 0 ]         in 3rd axis unit, (0,0)
      Channel label          MARK        [ velocity ]    [VELOCITY, FREQUENCY or
      Displayed field size   SIZE        [ 0 0 ]         in ANGLE_UNIT
      Field center           CENTER      [ 0 0 ]         offset in ANGLE_UNIT
      Cross size at center   CROSS       [ 2 ]           in arcsec, 0 ==> none
      Fields layout          DO_FIELDS   [ NO ]          (for Mosaics)

      Colour Scale range     SCALE       [ 0 0 ]         (0,0) ==> all dynamic
      Contour levels         SPACING     [ 0 Units]      (0) =+> Guess
      Spacing type           SPACE_TYPE  [ AUTO]  [LIN, LOG or USER]
      Side Display           SHOW_SIDE  [ NO ]

    SHOW also uses the (user-defined, optional) variable
    overlay_com       " " Command to be executed to add informations on Maps.