Gnuplot is free plotting software available for UNIX, Macintosh and Windows machines. It is an interactive package. The basic idea behind the program is to read in simple files of numbers and plot them. The files of numbers contain two columns, one for the abscissa and one for the ordinate. Preplot takes care of reformatting the output of the analysis so that Gnuplot can read the results and plot them. We have placed copies of Gnuplot for the three platforms on our ftp server.