1 Language
                             GTVL\ Language Summary

    CHANGE      : Change some attributes of the plot.
    CLEAR Arg   : Clear (some parts of) the plot or windows.
    COMPRESS    : Remove invisible parts of the plot.
    CREATE Arg  : Create directory, windows or LUTs.
    DESTROY Arg : Destroys (some parts of) the plot or windows.
    DEVICE      : Open the graphic device.
    DISPLAY     : List some parameters of the plot.
    GTV SEARCH  : Search for a GTV directory.
    HARDCOPY    : Get a printed copy of the plot.
    LENS        : Call the lens on the active window.
    LUT [arg]   : Change the color Look-Up-Table.
    METACODE    : Save or load part of the plot to/from metacode file.
    REFRESH     : redraw all or some windows
    REPLICATE   : Copy a directory to another place.
    ZOOM        : Zoom on the plot (possibly in another window).
1 CHANGE
        [GTVL\]CHANGE Item SegName Value [Val2 [Val3]]
        [GTVL\]CHANGE Behaviour Value

    Changes  some  attribute  of  the Graphic Library. Two items concern the
    current directory and active windows:
      - CHANGE DIRECTORY DirName [WinNum]
          changes the default directory to DirName, and optionally  the  ac-
          tive window number to WinNum (instead of 1) within this directory.
          The current working directory is stored as a character  string  in
          the SIC variable GTV%PWD.
      - CHANGE WINDOW WinNum|ZOOM
          changes  the active window number to WinNum or to the ZOOM window.
          The active window is in particular the one in which the cursor ap-
          pears for commands which use it.

    Some other items are image segment attributes:
      - CHANGE SCALING    SegName LIN|LOG [Lcut [Hcut]]
          will change the transfer function for the specified image segment.
      - CHANGE BLANKING   SegName BLACK|WHITE|Colour
          will change the colour of blanked pixels (if any) in the displayed
          image. Colour is a colour value as in PENCIL command (1-8).
      - CHANGE COLOUR     SegName Value
      - CHANGE DASH       SegName Value
      - CHANGE DEPTH      SegName Value
      - CHANGE VISIBILITY SegName ON|OFF
      - CHANGE WEIGHT     SegName Value
    The  last  five items are general segment attributes. For these, if Seg-
    Name is a segment, only that segment is modified, but if it is a  direc-
    tory,  all segments attached to this directory are modified accordingly.
    See subtopic SEGMENT_NAMES for details on naming segments.

    And finally, some general behaviours can be changed will  the  following
    keywords:
      - CHANGE LUT STATIC|DYNAMIC
          toggles  the  Look-Up-Tables to STATIC or DYNAMIC mode. Default is
          DYNAMIC. See subtopic LUT for details.
      - CHANGE PENCIL HARD|SOFT
          specifies whether the GTV library should use  the  (output  depen-
          dent)  hardware  generator for dashes and thickness, or whether it
          should use its own (output independent) software emulation.  Hard-
          ware  generator  may (or may not) produce nicer output, and may be
          faster...
      - CHANGE POSITION
          changes the window position on the screen. See  subtopic  for  de-
          tails.
2 LUT
        Specifies  whether  the  color Look-Up-Tables (LUT and LUT /PEN) are
    static, i.e. associated with each  graphic  segment,  or  Dynamic,  i.e.
    controlled by the terminal colors. This changes the behaviour of the LUT
    and LUT /PEN commands.

    In STATIC mode, each graphic segment has its own LUT, so that  this  al-
    lows  to  display  complex  plots with many colors. The LUT and LUT /PEN
    which are stored with each segment must be set before the  segment  cre-
    ation.  It cannot be changed after. In this mode, the display may differ
    from the hardcopy output, because not all interactive  displays  support
    many colors.

    In  DYNAMIC  mode,  one single LUT its associated to the plot. It can be
    changed dynamically afterwards using the LUT (and LUT /PEN) commands. It
    is  appropriate  for interactive visualisation. The hardcopy output will
    be identical to the display.

    The default is DYNAMIC.
2 POSITION
        CHANGE POSITION Num
        CHANGE POSITION Posx[Unitx] Posy[Unity]

    The first syntax moves the current window  to  the  specified  position,
    where  Num  is  in  the  range  1-9. The 9 most remarkable points of the
    screen (corners, middle of the sides, and center) are numbered according
    to a VT100 numeric keypad notation.

    The second syntax moves the current window to the specified coordinates.
    The recognized units are 'p' for pixels, and  '%'  for  percent  of  the
    screen size. Units default to 'p' if they are omitted.
2 SEGMENT_NAMES

        The  'SegName'  used in all the CHANGE commands is formed by a name,
    given by the calling high-level program (usually a reminder of the  com-
    mand  used), followed by an unique, incremental, number. To refer a par-
    ticular segment, one uses the full name  (as  in  CHANGE VISIBILITY CON-
    TOUR:46 OFF).  To refer to ALL the segments with the same name, omit the
    number (as in CHANGE VISIBILITY CONTOUR OFF). To refer  to  a  range  of
    segments,  use a 'minus' sign in the range (as in CHANGE VISIBILITY CON-
    TOUR:32-46 OFF).  Segments  names  can  be  the  segment  name,  as   in
    CHANGE VISIBILITY *TOUR OFF).
1 CLEAR
        [GTVL\]CLEAR [Arg [Value]]

    CLEAR without argument performs a CLEAR ALL, i.e. it empties all the top
    directories and thus their associated windows.

    Consult the following sections for the various CLEAR arguments.
2 ALL
         CLEAR ALL

    Performs a CLEAR DIRECTORY on all the top  directories,  i.e.  they  are
    emptied and their attached windows are cleared.
2 DIRECTORY
         CLEAR DIRECTORY [DirName]

    Empties  the named directory (or by default the current directory), i.e.
    remove the segments and subdirectories it contains.  As  a  consequence,
    under X, the windows attached to input directory are also cleared.

    If  the  subdirectories had windows attached, they are destroyed in con-
    junction to them. If the current working directory has to be  destroyed,
    i.e.  it  is  a  subdirectory  of the directory to be cleaned, it is im-
    plicitely moved to the latter.
2 SEGMENT
         CLEAR SEGMENT [SegName]

    Without argument, CLEAR SEGMENT destroys the last graphic segment of the
    current  directory,  i.e.  in  simplest case the part of the plot corre-
    sponding to the last graphic command. It can be used repetitively.

    CLEAR SEGMENT SegName makes destroys the named segment.One can  erase  a
    range  of graphic segments in a single command by typing a range of seg-
    ment numbers, as in CLEAR SEGMENT 24-16. See command GTVL\CHANGE for de-
    tails.
1 COMPRESS
        [GTVL\]COMPRESS

        Compress  the  internal metacode, by removing all the invisible seg-
    ments and directories.
1 CREATE
        [GTVL\]CREATE Argum Value [options]

    Creates either a directory, a window, or a Look Up Table stored  in  the
    metacode.
2 DIRECTORY
        CREATE  DIRECTORY PathName [/PLOT_PAGE SizeX SizeY] [/GEOMETRY Args]
    [/POSITION Args]

    Create a new directory. PathName syntax follows  "Unix-like"  pathnames,
    with  the  use  of  token '<' instead of '/'. Constructs like ..<Dir are
    valid.

    To create a new directory tree (called e.g. NewTop), use  the  following
    syntax:
        CREATE DIRECTORY <NewTop

    The  plot  space size of a new directory tree can be customized with the
    option /PLOT_PAGE. This option can not be used to create subdirectories,
    since they inherit the plot space size of their parent directory.

    Under X, a new window is implicitely attached to a new top directory be-
    ing created. Its geometry and position can be customized through the op-
    tions  /GEOMETRY  and /POSITION respectively. See HELP CREATE WINDOW for
    syntax and creation rules. These options are  illegal  when  creating  a
    subdirectory (for which no window is attached at creation time).
2 LUT
        CREATE LUT

    Store  the  current Look Up Table into the internal metacode. This makes
    sense if the LUT behavior is static (see HELP CHANGE LUT), so  that  the
    next graphic segments will use the last LUT stored in the metacode.
2 PENLUT
        CREATE PENLUT

    Store the current pencil colors into the internal metacode.
2 WINDOW
        CREATE  WINDOW  [BLACK|WHITE]  [NAME  Name]  [/GEOMETRY Sizex[Unitx]
    Sizey[Unity]] [/POSITION Posx[Unitx] Posy[Unity]]

    Create a new window seeing the content of the  current  directory,  with
    the corresponding attributes of background colour and Name. This command
    is only available under X.

    The window geometry is set:
    - if the option /GEOMETRY is present, to the values given  to  this  op-
      tion,  recognized  units  being 'p' for pixels, '%' for percent of the
      screen size, and 'r' for a fraction (aspect ratio) of the  other  size
      (units default is 'p' if omitted),
    - else,  to  the  values  read in the SIC logical named WINDOW_GEOMETRY,
      with the same syntax used for the option /GEOMETRY, if this SIC  logi-
      cal exists,
    - else, to the internal default values.

    The window position on the screen is then ruled:
    - if  the  option  /POSITION is present, by the values given to this op-
      tion, recognized units being 'p' for pixels or '%' for percent of  the
      screen size (units default is 'p' if omitted),
    - else, by the choice of the window manager.

    For example:
        GREG> CREATE WINDOW /GEOMETRY 400 2r
    creates a window of size 400 x 800 pixels, and
        GREG> CREATE WINDOW /POSITION 100% 100p
    creates a window aligned on the right and 100 pixels above the bottom of
    the screen.
1 DESTROY
        [GTVL\]DESTROY ALL|DIRECTORY|WINDOW [Values]

    Destroys (parts of) the plot tree and/or the windows seeing it.
2 ALL
        DESTROY ALL

    Destroys all the plot, i.e. destroys all the top directories  and  their
    windows.

    Since  the user can not be in the root directory (<) and create segments
    in it, a new top directory and its first window are implicitely  created
    after this. DESTROY ALL is thus the way to reset the tree and windows to
    their startup status.
2 DIRECTORY
        DESTROY DIRECTORY [DirName]

    With a directory name as argument, completely suppress the input  direc-
    tory  and  its windows (if any). If the current working directory has to
    be destroyed, it is implicitely moved  to  the  first  parent  directory
    which is not destroyed.

    Without  argument, completely suppress the last subdirectory of the cur-
    rent working directory.
2 WINDOW
        DESTROY WINDOW [DirName [WinNum|ZOOM]]

    DESTROY WINDOW DirName destroys all the windows attached  to  the  input
    directory. DirName defaults to the current directory.

    If  a  window number is given, only the window identified by this number
    in Dirname is destroyed. The keyword "ZOOM" can be used as an alias  for
    the zoom window in this directory, if any.
1 DEVICE
        [GTVL\]DEVICE [Dev_Type [Mode]] [/OUTPUT Dev_Name]

    Without argument, DEVICE displays the current working graphic device.

    With a graphic device type as argument, directs the graphic output to it
    and sets default values for the plot region location and device physical
    limits.  The basic unit is 1 cm for hardcopies. All plots to interactive
    devices are made with some pre-computed factor to match the screen  size
    to  the Plot Page size, defined by command SETPLOT_PAGE (default size is
    an A4 format page, 30 by 21).

    Use DEVICE ? to get the list of recognized graphics  devices  or  DEVICE
    type ? to get the list of modes on a given device.

    /OUTPUT Dev_Name option allows you to direct the graphic output to some-
    thing else than your own terminal (TT:). Note that some specific devices
    will  not  support  this option: this is currently the case for X-Window
    devices.
1 DISPLAY
        [GTVL\]DISPLAY Item [Arguments]

    List the internal parameters of the named item:
      DISPLAY DATA SegName
        shows the data values in input segment. For debugging purpose.
      DISPLAY DIRECTORY
        shows the current directory and its active window, if any.
      DISPLAY POINTER [SEGMENT|TREE]
        shows the internal values of the pointers. For debugging purpose.
      DISPLAY SEGMENT [SegName]
        shows the attributes of input segment (either a leaf or  a  directo-
        ry). Default is current directory.
      DISPLAY TREE [DirName]
        shows the directory tree in a recursive way. Default lists from cur-
        rent directory.
      DISPLAY WINDOW
        shows the active window and its attributes.
1 FLUSH
        [GTVL\]FLUSH

    Flush the internal stack. This could be useful when creating  a  complex
    plot  (stored in the metacode) and when the graphic device is late (when
    reading the metacode). Then you may want to force  the  synchronization:
    FLUSH  will  return only when all the instructions in the stack are exe-
    cuted.
1 GTV
        [GTVL\]GTV SEARCH DirName

    If the GTV directory DirName exists,  sets  the  variable  GTV%EXIST  to
    .TRUE., e.g.

    GREG> GTV SEARCH <GREG
    GREG> EXAMINE GTV%EXIST
    GTV%EXIST       = T              ! Logical GLOBAL
1 HARDCOPY

        [GTVL\]HARDCOPY  [File] [/DEVICE Name [Attributes]] [/PRINT Printer]
    [/DIRECTORY DirName] [/GEOMETRY  Sizex[Unitx]  Sizey[Unity]]  [/FITPAGE]
    [/EXACT] [/OVERWRITE]

    Creates  (and  optionally send to a printer) a "hardcopy" of the current
    plot.

    The default behaviour is to scale the GreG PLOT_PAGE (centimeters)  into
    the output physical page. This can be overriden with the two options:
    - /EXACT: 1 cm on the GreG PLOT_PAGE will be 1 cm on the hardcopy physi-
      cal page, for devices for which it makes sense,
    - /FITPAGE: the plot will be automatically rotated and  scaled  to  make
      the  best  use  of  the  hardcopy physical page. The option /PRINT im-
      plicitely enables this feature. See subtopic for details.
    These two options are exclusive.

    The /DEVICE option argument specifies which  type  of  plotter  will  be
    used.  See  the  subtopic /DEVICE for a list of the allowed devices. The
    other arguments passed to this option can modify the attributes  of  the
    hardcopy.  If the option is not used, the harcopy device defaults to the
    content of the SIC logical GAG_HARDCOPY.

    The /DIRECTORY option allows to specify which GTV  directory  should  be
    sent to the hardcopy. Without this option, default is current directory.

    The /PRINT option is used to force immediate printing  and,  optionally,
    to  control  which  printer should be used. Printer is the printer name,
    which defaults to the content of the SIC logical GAG_PRINTER. The print-
    ing  command  is  ruled  by the SIC logical GAG_LPR. If no file name was
    specified for an immediate printing, the metacode file is deleted  after
    print completion, otherwise it is kept.
2 /DEVICE
        [GTVL\]HARDCOPY [/DEVICE Name [Attributes]]

    The /DEVICE option argument specifies which type of device will be used.
    The other arguments passed after the device name can modify the  harcopy
    attributes.  Several attributes can be combined. Allowed devices and at-
    tributes are:

      PS (PostScript): the plot is automatically rotated and scaled  on  the
              hardcopy physical page.
        GREY  PostScript  with fixed greyscale transfer function for bitmap.
        COLOR PostScript with user controlled color transfer function.  This
              is the default.
        FAST  PostScript  with  hardware pen thickness handling. Clipping of
              wide pens may be inaccurate. This is not the default.

      EPS (Encapsulated PostScript): As PS, with  the  BoundingBox  computed
              from  the plot boundaries rather than from the Plot Page size.
              The plot is NOT rotated neither scaled to the hardcopy  physi-
              cal  size  by  default. Use the option /FITPAGE to enable this
              feature.
        GREY  Same as PS.
        COLOR Same as PS.
        FAST  Same as PS.

      PNG (Portable Network Graphics): create a bitmap representation of the
              GreG  plot.  The  size of the PNG can be tuned with the option
              /GEOMETRY.
        GREY  Same as PS
        COLOR Same as PS
        WHITE PNG with white background and black foreground.  This  is  the
              default.
        BLACK PNG with black background and white foreground.
        TRANSPARENT  PNG  with transparent background. This is not exclusive
              with WHITE and BLACK attributes, i.e. "TRANSPARENT BLACK" cre-
              ates  a  PNG with transparent background and white foreground.
              Transparency is not activated by default.
        NOBLANK Blanked pixels will not be drawn, i.e.  they  will  use  the
              background  color  (white, black, or transparent) or they will
              let you see previous drawings made behind.
        CROPPED the GreG plot is expanded to fit exactly to the best PNG di-
              mensions,  and the other PNG dimension is shrinked to leave no
              margin.

      SVG (Scalable Vector Graphics): create a vectorial  representation  of
              the GreG plot (except for images) in the SVG format.
2 /FITPAGE
        HARDCOPY /FITPAGE

    Automatically  rotate and scale the desired part of the plot to match at
    best the hardcopy physical size. Alternatively, the variable GTV%FITPAGE
    can be set to YES to force this feature.

    The  desired  part of the plot is the full Greg plot page for PS, or the
    cropped plot for EPS. The hardcopy physical page is controled by the sic
    logical GAG_PAPER_SIZE set at compilation time.

    In  the  case of PS/EPS hardcopies, if the plot actually needs rotation,
    the line "%%Orientation:  Landscape"  or  "%%Orientation:  Portrait"  is
    added  in  the  PostScript header. This line is recognized by PostScript
    viewers (e.g. ghostview) so that they unrotate the file when  displaying
    it.  On  the other hand, empirical tests show that Latex, MS/Open/Libre-
    Office, or eps2jpg ignore it. Hopefully, printers also ignore this line,
    giving this option its full sense.
2 /GEOMETRY
        HARDCOPY /GEOMETRY Sizex[Unitx] Sizey[Unity]

    The  /GEOMETRY option allows to customize the size of the hardcopy. This
    option is supported on the following devices:
    - PNG: units allowed are 'p' (pixels) and 'r' (aspect ratio). Units  de-
      fault to 'p'.

    Without  this option, the hardcopy size can be ruled through the follow-
    ing SIC logicals, using the same syntax as above:
    - PNG_GEOMETRY

    If neither the option is used nor the SIC logical is set, then the hard-
    copy size is defined with internal default values.
2 /OVERWRITE
        Existing  hardcopy  files are not overwritten, but the option /OVER-
    WRITE can be used to force this. Alternatively, the variable  GTV%NOFAIL
    can be set to YES to force overwriting.
1 LENS
        [GTVL\]LENS

    Under  X,  call  the  lens on the active window. The flow of commands is
    suspended until the lens is closed.

    The usual way to call the lens is using the middle-click of the mouse on
    the  plot. However, this command is useful to give a detailed look to an
    intermediate plot during a procedure, since it acts like a PAUSE.

    When opened, the lens is controled by the following actions:
      - Mouse wheel: reduce or enlarge the zooming factor,
      - Left-click or CTRL+wheel: reduce the lens area,
      - Right-click or CTRL+wheel: enlarge the lens area,
      - Middle-click: close the lens
1 LUT
        [GTVL\]LUT [Argum] [/PEN] [/REVERSE]

    Modify the bitmap or pen look up table. Option /PEN indicates to  modify
    the  value  of the 16 user-controlled pen colors (colors 8 to 23) rather
    than the bitmap look-up table.

    The default argument is LUT. Possibles arguments are:
    - ?
        Type "LUT ?" to display the list of available LUTs. One can use  al-
        ternatively  the  LUT  editor (button "Edit Lut") to browse and edit
        the LUTs in an interactive widget.
    - DEFAULT
        Load the default color table.
    - COLOR
        Load a color table with a circular hue value, from red to red.
    - BLACK
        Load  a  black  and  white  color  table  (white  background,  black
        sources).
    - WHITE, RED, GREEN, BLUE, MAGENTA, YELLOW, CYAN and NULL
        Load  a  color table with black background and sources in the corre-
        sponding color (NULL is fully black).
    - LUT
        Load the color table defined by an HSV (HUE, SATURATION  and  VALUE)
        or  RGB (RED, GREEN and BLUE) color model. There are six user-write-
        able SIC variables named  LUT%HUE,  LUT%SATURATION,  LUT%VALUE,  and
        LUT%RED,  LUT%GREEN  and LUT%BLUE that contain the HSV and RGB model
        of the current LUT. These arrays values  can  be  manipulated  using
        standard  SIC mathematic functions to create new Look-Up Tables (see
        below). Depending on the value on LUT%MODE, the model is  read  from
        the HSV (LUT%MODE.eq.1) or from the RGB (LUT%MODE.eq.2) arrays.
    - Any other LUT Argum will read Red Green Blue values from the formatted
        file named "Argum". See subtopic FILE for details.

    A convenient value for the hue array is
            LET LUT%HUE[I] = 256*(1-(I/LUT%SIZE))
            LET LUT%SATURATION 1
            LET LUT%VALUE 1
            LUT LUT
    which is a "classical" color table from blue to red as used in AIPS  for
    example. Color contours can be obtained using variations around the fol-
    lowing command:
            LET LUT%HUE[I] = 16*INT(256*(1-(I/LUT%SIZE))/16)
    and so on with the most funny functions you may invent.
    CAUTION: the hue is a real number between 0.0 and 360.0

    The LUT, whereever it comes from, can be reverted before  use  with  the
    option /REVERSE.

    Note  that  a  similar  behaviour is defined for the BLANKING color (the
    color used to paint blanked  pixels  in  images),  with  the  six  reals
    LUT%BLANK%HUE, LUT%BLANK%SATURATION, LUT%BLANK%VALUE, and LUT%BLANK%RED,
    LUT%BLANK%GREEN, LUT%BLANK%BLUE.
2 /PEN
        Same behaviour as LUT, but will update the colors  of  the  16  pens
    (colors 8 to 23) used for contour-filling.

    The associated HSV and RGB models can be found and customized in the sic
    arrays  named  LUT%PEN%HUE,   LUT%PEN%SATURATION,   LUT%PEN%VALUE,   and
    LUT%PEN%RED, LUT%PEN%GREEN and LUT%PEN%BLUE, one or the other being used
    depending on the LUT%MODE value.
2 FILE

        The command LUT can read the colormaps from a formatted file. A var-
    ious  number  of  these  files is already available in the distribution.
    Type "LUT ?" to see these files.

    The files are searched in the  path(s)  contained  in  the  SIC  logical
    LUT#DIR:. It can be a collection of paths customized by the user. By de-
    fault LUTs are searched in the current directory and in GAG_LUT:  (where
    the standard GTV LUTs are stored). The default extension is ".lut".

    User  can define and save its own LUT in such a file. The formatted file
    must be an ASCII file providing the three R,  G  and  B  intensities  in
    three  columns,  and there must be as many lines as color levels needed.
    The intensities are three real numbers between 0.0 and 1.0.

    The LUT loaded from such a file will then be resampled (using interpola-
    tion)  to  match the effective number of colors the device supports. For
    example, the file example.lut:
    shell> cat example.lut
         .00000    .00000    .00000
         1.0000    .00000    .00000
    will produce a black to red color map, with continuous color levels  be-
    tween.
1 METACODE
        [GTVL\]METACODE EXPORT|IMPORT FileName [DirName] [/PATH PathName]

    Allow  to  save  or load whole or parts of the current plot to or from a
    metacode file.
2 EXPORT
        [GTVL\]METACODE EXPORT FileName [DirName]

    Export the current (or specified) directory tree to an external metacode
    file of name FileName. The default extension is .meta . The sub-plot can
    later be reincorporated  using  command  METACODE IMPORT.   This  allows
    merging several plots together.
2 IMPORT
        [GTVL\]METACODE IMPORT FileName [DirName] [/PATH PathName]

    Insert an external metacode file at the specified PathName into the cur-
    rent plot. PathName defaults to the current directory.
1 REFRESH
        [GTVL\]REFRESH [DirName [WinNum|ZOOM]]

    By default, redraw all windows in all directories. If a  directory  name
    is  provided, redraw the windows seeing this directory and its subdirec-
    tories. If a window number is also specified, redraw only  this  window.
    The  keyword  "ZOOM" can be used as an alias for the zoom window in this
    directory, if any.

    The windows are drawn and redrawn as soon as new segments are added,  or
    if the window manager requires it (e.g. window is resized). However, for
    efficiency purpose, segments are first drawn one onto the previous ones,
    in  the chronological order. Depending on their depth (e.g. images which
    are by default at depth 2), this is not what happens in  the  subsequent
    redraws and in hardcopies. In this case, it makes sense to force the re-
    fresh of a window.
1 REPLICATE
        [GTVL\]REPLICATE Dir1 Dir2

    Copy Dir1 subtree to Dir2 subtree. Not very useful now, but will  become
    interesting  when  shifting,  stretching, rotations, and user coordinate
    changes will be allowed for all segments.
1 ZOOM
        [GTVL\]ZOOM [X1 X2 Y1 Y2 | OFF]

    The command ZOOM opens or closes a new window which displays  a  smaller
    region  of  the current plot. Each plot can have its own zooming window.
    It will be reused by subsequent calls to the command ZOOM.

    Without arguments, ZOOM calls the cursor to  define  the  viewing  area.
    This  area  will be defined by its center (at the cursor position) and a
    zooming factor (by steps of 1.414):
       Z       Increase the zooming factor
       -       Decrease it
       0       Reset it
       E       Exits from the routine
    These commands do not produce effective zooming, press the space bar  to
    do  it. For X11 displays, you may use the mouse buttons for the commands
    <Space> (left mouse button), Z (middle mouse button), and E (right mouse
    button).

    ZOOM X1 X2 Y1 Y2 can  be used to define the viewing area by a non-inter-
    active mean. The values must be in paper units (cm).

    Use ZOOM OFF to close the zoom window of the current plot, if any.
1 ENDOFHELP


















