I tried the unit by putting it inside an mw-oven and watched the meter through the frontglass.
I saw the needle moving but after 1 or 2 seconds the circuit burned out. The resistor was blown-up. So it appears to work somehow.
That reminds me.. when I was a little boy, my friend were told by his dad to buy a box of matches, "and make sure they are good matches" were the concise instruction. So he lit every one of the matches in the box to make sure they works..
Daymn, but that was a long long time ago..