Got new used car with new used radio

Regarding balance and fade contols, which pop out for adjustment and
then can be pushed in, so that only a little sticks out:

"Adjust the balance (or fade, for the other button) and push the button
back in. The balance (or fade) will be displayed and continuously
updated while the button is pressed".

What does this mean?

How can it update the fade or balance setting? Is the knob not a direct
adjustment but something that controls an electronic circuit? I can see
that could be, but what standards would it use for modifying the balance
and fade? Would it use sensors to tell which seats are occupied? I've
thought about that for years** but if any car did this, I'd have thought
I would have heard about it.

Right now, both adjustments are in the middle, and maybe I'd see
something on the display if I turned one of them, but I'm asking here
first.

**GM cars did and maybe do use the Right Rear speakers to provide the
same channel as the Left Front (and Left Rear and Right Front had the
Right channel) and they did this to make up for the fact that almost
everyone sits in a corner of the car. I had GM cars for 21 years
although maybe the first ones (1965) didn't have a stereo radio? I'm
sure the '67 and '73e did and the sound was fine.