websearch brings up exactly one mention and a picture:http://www.museo-cb.com/museo-cb/medidores-roe/asahi-seyko-sangyo-meiix/
Lited there as: CB, AM:max 100 watts
Click on the little picture for a blowup.
Power meter on L, SWR on R.
At the top of the Power Meter is a "SET" mark. You key down and turn the knob until the meter needle is there, then read the SWR on the RH meter. This is a guess.
Since the Power meter has two scales, 0-10 and 0-100W, there has got to be some switches somewhere on the thing? Maybe not, maybe the knob attenuates enough to cover both scales. In that case, good idea to alway start off with knob turned all the way down so as not to slam or pin the meter movement.
Have you removed the cover and taken a peak inside?
This might be a good quality stripline meter, well, as good as stripline gets.