-v power usage 
-t [Power] Waschmaschine
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DEF:U=/var/www/mrtg/rrd/keller-waschmaschine.power.rrd:ds0:AVERAGE
DEF:I=/var/www/mrtg/rrd/keller-waschmaschine.power.rrd:ds1:AVERAGE
CDEF:P=U,I,*
COMMENT:        max.          avg.         min.         cur.\n
AREA:P#F5790060:Power
GPRINT:P:MAX:%6.2lf %sW
GPRINT:P:AVERAGE:%6.2lf %sW
GPRINT:P:MIN:%6.2lf %sW
GPRINT:P:LAST:%6.2lf %sW\n