instructions use a language called B<RPN> which is described in its
own manual page.
+Variable names (I<vname>) must be made up strings of the following characters
+C<A-Z, a-z, 0-9, -,_> and a maximum length of 255 characters.
+
+When picking variable names, make sure you do not choose a name that is
+already taken by an RPN operator. A save bet it to use lowercase or
+mixedcase names for variables since operators will always be in uppercase.
+
=head1 DEF
B<DEF:>I<E<lt>vnameE<gt>>=I<E<lt>rrdfileE<gt>>:I<E<lt>ds-nameE<gt>>:I<E<lt>CFE<gt>>[:step=I<E<lt>stepE<gt>>][:start=I<E<lt>timeE<gt>>][:end=I<E<lt>timeE<gt>>][:reduce=I<E<lt>B<CF>E<gt>>]
Example: C<VDEF:avg=mydata,AVERAGE>
+Note that currently only agregation functions work in VDEF rpn expressions.
+Patches to change this are welcome.
+
=head1 CDEF
B<CDEF>:I<vname>=I<RPN expression>
=head1 AUTHOR
-Program by Tobias Oetiker E<lt>oetiker@ee.ethz.chE<gt>
+Program by Tobias Oetiker E<lt>tobi@oetiker.chE<gt>
This manual page by Alex van den Bogaerdt E<lt>alex@ergens.op.het.netE<gt>