Ok…well…you have a few options depending on how your know rotates.
Lets imagine a clock face with A at 10, B at 12 and C at 2…. is this sort of what you are trying to solve or is it something more complicated… like A is 2 full turns, B is 3 full turns and C is four full turns?
For simplicity I will explain your options with A at 10 , B at 12 and C at 2.
You do not need shape keys or any animation in blender.
You can use the WhenDrag Over and drag rotate puzzle in V3D and use the get object rotation value and set object rotation value. You will use the get object rotation value to see if the knob is in the general range of the either -60 degrees for 10 or 0 degrees for 12 or +60 degrees for 2.
You can have it snap in to place if the range of rotation is with +/- 10….things like that.
If you need to count rotations…. this is a current problem since rotations are 0 to 180 then -180 to 0…not actually counting rotational values like you have in blender. I am working on that script now.
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