[mirimir]

Ah, so a slider, posing as a knob.

[royjacobs]

Yes, except taking up much less space.

[setr]

Which is exactly the purpose of a knob in meatspace too :)

[mirimir]

Right. Physically, potentiometers are semicircular sliders.

But another advantage of knobs is the ability to turn them, quickly and yet accurately, with thumb and first finger. Some even have push-pull gear reduction, to go between fast and accurate.

So you'd think that a GUI knob would use some analogous two-finger twisting gesture. With thumb and first finger.