[jacobolus]

> actions like turning/twisting do not work well on touch screens

Have you ever used an iPod (capacitive touchpad) scroll wheel?

A good physical knob is still better, but a touch wheel can be made pretty decent.

[sgustard]

The iPod wheel has a physical barrier acting as an affordance for your finger to trace. It certainly works better than it would just floating in space in the middle of a touch screen.

[gugagore]

I wonder if it's much easier to process the signal (at the level of measuring and interpreting the capacitances) if you assume a one-dimensional user input. I'm not sure what signal processing happens when sliding on a touchscreen/trackpad.

[PhasmaFelis]

A iPod touchwheel can be used without looking at it. It's much more like a knob than a touchscreen display, even if it uses similar technology.