I have a Elto EMA-1 power meter made by Cixi Yidong Electronic Co Ltd which looks the same apart from the plug pins (different shape here).
A word of warning about these meters - beware the smell of burning if used to monitor a modified sine inverter and a sudden drop of reading to zero!! Dismantling revealed a very charred resistor.
The measurement part of the meter gets its power from the line (the display is from the 2 button cells). It does this with an R-C network that relies on the waveform being a sine wave to determine how much current passes through the 'C' part of the circuit. Apply the fast edges of a modified sine inverter and the 'R' part gets cooked.
In case anyone else has this problem, I emailed the manufacturers in China and was very pleased to receive a response in less than a week that the resistor should be 150 ohms. Comparing a friends unit which had a 100ohm resistor fitted, I ended up putting in 120ohm but upgraded from a 0.5 watt to 2 watt.
I've not tried it on the inverter again but at least I can use in on my grid stuff again :-)
