3. DATA INPUT


   XY PLOTTER allows you to enter a maximum of three data sets.  These
sets may be typed in from the terminal, or be defined in external files
before XY PLOTTER is executed.  The sets MUST contain real values, and
may consist of as many as 1000 pairs per plot.  If a file exceeds 1000
pairs, the excess data will not appear in the plot, and the user will
be warned.  Alternately, a file must contain at least two points, since
the package will not plot a single point.  Data input obtained from the
keyboard option may be saved in external files.

   Additionally, if the user specifies that he would like to read
(or enter) data for up to three curves at the same time, XYPLOT 
assumes the data will be entered (read) like so:




X-value   Y1-value   Y2-value   Y3-value
-------   --------   --------   --------
  9.4       16.12      18.76      13.21
 10.6       14.12      18.54      27.43
 12.6       23.2      109.122     37.0
  .          .          .          .
  .          .          .          .
  .          .          .          .

This would generate three different curves, Y1, Y2, and Y3.
Notice that they all must share common X values.
