[rrd-users] PREV-Function? SUM-CF ?

[Rene Fritzsche]

Hi.

First of all, let me explain, what i'm planing to do:
i've got some data of a lightsensor, measuring the
irradiation. these values are measured in watt/m^2
and are fed into a rrd-database every 60 seconds.

now i want to calculate the amount of energy in total
which is collected by this sensor since a chosen time...
measured in watt*s.
(i know the size of the surface area of that sensor.)
and i dont want only one value for a day, i want to
have the run of the curve of the energy.

So what i really need is a function to integrate the
function of received energy.
Here is what i tried to do to build the sum of all
values of the past: [using rrdtool graph]

DEF:Ls=Light.rrd:D1:AVERAGE
CDEF:E=PREV,Ls,60,*,+
LINE:E#FF0000

but it wont work .. E is allways 0 or not defined [i dont
see any line]. i think the PREV-Function isnt working for
non "DEF-Values"..inconsistent with the manual-page.

using
VDEF:E=Ls,TOTAL

gives me only one constant value for the whole graph
-  but not the curve.

Can you help me?

PS: I think a SUM-ConsolidationFunction could be useful
for problems like this..

Yours, Rene.

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