measuring THD with vintage AWA-F240 Distortion/noise meter.

[ErwinsCat]

HI, I'm trying to measure the THD with an old Distortion & Noise Meter AWA-F240  http://www.smoke.com.au/~ic/audio/AWA-F240.html
I am not sure how to read the analog meter! I'm assuming when the METER RANGE selector is in the "0dB/100%/1V" range, the number 10 in the second row in the display means 100% THD.
also if it was in noise meter, a number 3 in the scale  (3rd row) meant 1 volt of oRMS noise or +2dB because of the selector was  "0dB/100%/1V" range?

image1: the unit image
image2: meter detail
image3: output voltage/signal (i'm assuming this is the filtered out harmonics waveform )
image4: input voltage
image5: input/output signal

thanks