[rrd-users] merging 2 data sets onto 1 graph

[Mag Gam]

Newbie to rrdtool so I have been following this nic tutorial:
http://ds9a.nl/rrd-mini-howto/cvs/rrd-mini-howto/output/rrd-mini-howto.html#toc1

I have data like this:

on.csv
1269829313,5
1269829314,4
1269829315,3
1269829316,5
1269829317,7
1269829318,8
1269829319,2
1269829320,1
1269829321,3


off.csv
1269829313,10
1269829314,14
1269829315,20
1269829316,20
1269829317,20
1269829318,20
1269829319,14
1269829320,15
1269829321,17


I would like to merge this data and graph it into 1 graph.

So. here is what I did so far:
rrdtool create datafile.rrd --step 1 DS:on:ABSOLUTE:900:0:50 ....

Not sure how I can bundle the graph, any thoughts?

TIA