This is an audio power meter made
Useful for checking audio amplifiers
or the output from hi-fi equipment
Nothing special, it indicates up to
10watts RMS. I had a huge amplifier to repair the other day.
It cost a small fortune to fix as something like 10 MOSFET power
transistors driving one of its two channels had bitten the dust,
presumably when they saw a short-circuit and the owner had cranked
up the power wondering why nothing was happening. As the thing
was rated at a kilowatt per channel there must have been a fair
bit of smoke at the time.