The Gnuplot graphing utility

Gnuplot is a flexible graphing utility, with fairly useful online help.
How to save a plot was not easy to find, however.  Here are instructions.
The online manual is at this URL.
http://www.gnuplot.info/docs/gnuplot.html

To save plots:
At the gnuplot prompt
gnuplot>
enter the command
set terminal postscript
or 
set terminal latex
or 
set terminal fig
to format the plot as a postscript file, latex picture file, or xfig
file, respectively.  Then enter
set output "filename.xxx"
where xxx is ps, tex, or fig, as is appropriate.
Then enter
replot
This will send your last plot to the file filename.xxx in the format you
want.