this I<vname> in another B<RPN> expression, you are effectively
inserting its value just as if you had put a number at that place.
The variable can also be used in the various graph and print
-elements. I<Not yet implemented:> [ Everywhere you can insert a
-number, you can also use the B<VDEF> (provided that it is set of course) ]
+elements.
Example: C<VDEF:avg=mydata,AVERAGE>