[rrd-users] Dynamic Steps

[Alex van den Bogaerdt]

> Everytime one Watt/hour has been consumed, the power meter sends a signal 
> to the Raspberry Pi. By measuring the time between two signals, I'm able 
> to calculate the actual power consumption:

Are you not overthinking this?
A kWh (or a Wh if you really get thousand signals per kWh) is just a measure 
of the amount of Joules.

If you feed Joules to RRDtool, it will store Joules per second, which equals 
Watt.

All you have to take care of is that RRDtool receives at least one update 
within the heartbeat time.

Try the ABSOLUTE counter type, feeding 3600 (for Wh) or 3600000 (for kWh) 
every time you get a signal.

The resulting graph, without any tweaking, should be your power usage over 
time, shown in watt (or kilowatt, and so on)