Documentation here: http://wiki.erazor-zone.de/doku.php?id=wiki:projects:php:dokuwiki:plugins:gnuplot

Sample graph:

<code>
<plot>
plot [-2:20] 2*cos(x)
</plot>
</code>

<plot>
plot [-2:20] 2*cos(x)
</plot>

<plot>
set contour base
set cntrparam levels incremental -20,5,10
set title "9 incremental contours starting at -20, stepping by 5" 0.000000,0.000000  font ""
splot x*y
</plot>