[rrd-users] how to calculate the sum of a DS

Alex van den Bogaerdt alex at vandenbogaerdt.nl
Fri Jul 5 13:09:50 CEST 2013

----- Original Message ----- 
From: "stefan" <Stefan.Bruder at gmx.net>
To: <rrd-users at lists.oetiker.ch>
Sent: Friday, July 05, 2013 9:31 AM
Subject: Re: [rrd-users] how to calculate the sum of a DS

> Hi Alex,
> thank you for your explanation, but now I am little more confused.
> my PV controller gives me the power created ( example 400Watt) each 10
> seconds,
> so I have 400W/10s.

No.  It's not 40W every second. It's 400 (on average) Joules every second 
during 10 seconds.

That is: if your device indeed does report in Watt.

Also possible (and more likely) is that your device reports energy 
delivered, for instance in Wh.

If you confuse W with Wh, you won't get correct numbers unless by chance.

Make sure you understand the difference, and why it is watt multiplied by 
hour, not divided by hour.

> For my understanding I should take the sum of all value (where watt >0)

Why the ">0" restriction?

We'll get to the rest as soon as you figured out exactly what is reported: 
energy or power.

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