Measuring embedded asterisk power consumption

For sometime now i wanted to look at the power consumption of embedded devices running asterisk compared to a "standard" pc (if such a thing exists) and possible extend it also to measure standard PBX's.

With a first look it looks easy enough, but as with all measurements where you want an accurate result the devil is in the details.

First problem that has to be answered is "How do you get an accurate measurement of the power consumption"

There are several low-cost "energy metering devices" ( 15-20 Euros) in the market, in some cases you can find then in supermarkets also, but the accuracy they provide is rather dubious.
From a first look most could not measure power if the power was less than 5W, which is close to what a lot of embedded boards are rated at.
Also is very close to what most PC power supplies would consume in idle mode.

There are some professional equipment out there but spending 400-2500K Euros was not an option.
So after some search and reading i found a device that looks accurate enough and won't make a big dent on the budget.

This was Voltcraft Plus Energy Logger 3500 from Conrad.de


According to the specs it could measure :

Operating voltage 230 V/AC
Performance measurement display 0.1 -3500 W
Performance consumption display 0.000 - 9999 kWh
Display 3-cell with 4 positions each
Tariff range 0,000 - 9,999
Accuracy 5 - 3500 W (± 1% + 1 count)
2 -5 W (± 5% + 1 count)
less than 2W (± 15% + 1 count)

So it provides a +- 5% accuracy from 2-5 W which is rather good for a device that costs 50 Euros.

The other big advantage is that it uses an SD card to store measurements and comes with a piece of software to display the data captured.

I have placed an order for it and i expect it to arrive within next week.
That would give me enough time to figure out which devices and the way to test them.

Any ideas/suggestions/criticism is welcome.