B&W 802 Series 80

Can anyone tell me what the parameters are for the "Enviromental Control" settings A/B/C on the back of the midrange speaker. What there functions are and do? I have experimented briefly and have had a hard time hearing a difference.Thanks, spl.
Note, worked this out by some careful listening with a fine BIS recording on vinyl. Quite simple dynamically.
A=High Range
B=Moderate Range
C=low Range
The beauty of these older 802's and the dials is that they act as a very simple EQ for poor recordings on Class A preamps that have no EQ capability.