Originally Posted by
EEngr
This is much like a computer mouse, which has no idea where it is but sends the system up/down, left/right pulses and lets the software calculate from that. The latter is much easier to implement. A dual rate knob would simply check the rotation speed (clicks per second) and increment/decrement at a faster rate. All done in software.
A lot of mouse drivers have a dual rate function, above a certain speed the cursor move much farther for each pulse. Just checked mine and it is fairly obvious when fast mode kicks in.