X-Git-Url: https://git.octo.it/?p=rrdtool.git;a=blobdiff_plain;f=doc%2Frrdgraph_data.pod;h=c26868f0e509ffe00559f52922ae16a770d9daf2;hp=5b71c87f94b924c452fb3416a5cd5050cebcfaeb;hb=22129bb15a8ad204cf8a5e88e8834ec0b51908c0;hpb=26f7c5c1ba83c8ab82cd271b143061f7fb13394c

diff --git a/doc/rrdgraph_data.pod b/doc/rrdgraph_data.pod
index 5b71c87..c26868f 100644
--- a/doc/rrdgraph_data.pod
+++ b/doc/rrdgraph_data.pod
@@ -19,6 +19,13 @@ useful information such as maximum, minimum etcetera. Two of the
 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 safe 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>>]
@@ -27,7 +34,7 @@ This command fetches data from an B<RRD> file.  The virtual name
 I<vname> can then be used throughout the rest of the script. By
 default, an B<RRA> which contains the correct consolidated data
 at an appropriate resolution will be chosen.  The resolution can
-be overridden with the L<--step|rrdgraph/item_Time> option. 
+be overridden with the L<--step|rrdgraph/item_Time> option.
 The resolution can again be overridden by specifying the B<step size>.
 The time span of this data is the same as for the graph by default,
 you can override this by specifying B<start and end>.  Remember to
@@ -68,6 +75,9 @@ elements.
 
 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>
@@ -91,6 +101,6 @@ Make sure to read L<rrdgraph_examples> for tipsE<amp>tricks.
 
 =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>