[rrd-users] Modifying results for GPRINT output
Piers Kittel
mailing at biased.org
Sat Sep 1 18:56:54 CEST 2007
Hello all,
I have just installed a bunch of sensor stuff my friend made for me
to measure my electricity usage. The sensor tells the computer when
my electricity meter flashes, and a number in a text file is
increased by one. Every minute, the value is inserted in a RRD as a
counter. One flash from the meter represents 1/800th of a kW. I
modified my y axis to show the correct value - multiply by 1250 to
give watts (I don't know why I have to multiply by a thousand to give
watts, as if I multiply by 1.25, I can see a "m" in front of the
values). Anyway, I'd like to see the maximum, average and minimum
values at the bottom of the graph - I've discovered GPRINT, but it
shows the wrong value. For the life of me, I can't figure out how to
modify the values to show watts, instead of counts. Currently, the
graph shows a line going between 230 watts and 185 watts. The output
from GPRINT shows 0.18 for max, 0.17 for average and 0.15 for min. I
know I need to multiply those 3 values by 1250 to show the correct
figures, but how? I tried making a new variable and doing
calculations on it, but doesn't seem to work. The line in my script
to create the graph is:
rrdtool graph -w 800 -h 250 --vertical-label "Watts" /home/piers/
software/rrdtool/leccyday.png DEF:usage=/home/piers/software/rrdtool/
meter.rrd:meter:MAX CDEF:realusage=usage,1250,\*
LINE1:realusage#0000FF VDEF:usagemax=usage,MAXIMUM
GPRINT:usagemax:"Max\: %lfw" > /dev/null
I tried inserting a snippet "CDEF:usagemax2=usagemax,1250,*" but I
got "ERROR: rpn expressions without DEF or CDEF variables are not
supported"
What am I doing wrong here, and how do I fix this?
Thanks very much for your time!
Regards - Piers
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