Here, all the knobs are being controlled by rotating them. This is their default behaviour, and you can change it by setting the verticalDrag option to true, to use mouse dragging to controll their values. Rotation is mostly better suited for bigger widgets like these.
In this example, adding a background image (little dashes around the knob) is demonstrated on the 3 smaller knobs.
You can also incorporate your own tooltip, which I've done here to display the value of the knob that's currently being adjusted.
If you double-click on the pot, you can type in the precise value with your keyboard.