That's a bit different, it's got graduations on the knob. I'm thinking of a pure encoder-based system, where the absolute position doesn't matter but the change in position (and rate of change of position) do. Think like a mouse scroll wheel, but with acceleration.

That only goes up to 6 minutes though.

30 minutes involves a much more extreme change in distances... and then of course in the speed of the knob as the timer runs back down.