sf_vertical_slide   Place a vertical sliding button on the screen
------------------------------------------------------------------------------

    function dbl sf_vertical_slide prototype
      parameters value int top_row,;
                 value int bottom_row,;
                 value int collumn,;
                 value int hi_value,;          && Highest value allowed
                 value int low_value,;         && Lowest value allowed
                 value dbl start_value,;       && Value to start at
                 value dbl value_increment,;   && Increment ? per keystroke
                 value byte background_color,; && Window color slide is on
                 value byte button_color,;     && Button color ( suggest 007 )
                 const logical show_value,;    && Show the numeric value?
                 value int value_row,;         && at what row
                 value int value_center,;      && centered at ? collumn
                 value int value_format,;      && # of characters displayed
                 value byte value_color        && color of numeric display

    This function places a sliding button on the screen which the
    user can move  up/down to change the current value.  The
    slide terminates upon the user pressing the ENTER key thus
    selecting the current value.