4. WINDOW:

   The 'window' is that portion of the X-Y plane which will be
displayed.  The default dimensions of the window are the maximum
and minimum values of the data:


                      Ymax _________________
                           |               |
                           |               |
                           |               |
                           |               |
                      Ymin |_______________|
                           X              X
                          min            max



This will result in at least one data point being plotted on each
window border.  The window option allows you to choose the dimensions
of the window.  Only data points within the window will be displayed.
If the continuous plot option is used, lines through the window may
appear which intersect two points outside the window, as shown on the
next page ... 












                               / <---- not displayed
                           ___/_____________
                           | /             |
                           |/              |  Points falling outside
                           /               |  the window are not
    not displayed ----->  /|               |  plotted.
                         / |_______________|

                           _________________
                           | /             |
                           |/              |
          displayed plot   |               |
                           |               |
                           |_______________|




Obviously, maximum and minimum values may not be equal, therefore a
slight offset is implemented when a vertical or horizontal line has
been input.
