jQuery Knob is a lightweight jQuery plugin for creating good-looking circular switches (like the "volume controls" in radios).
It works by transforming any given input fields according to the values defined in its attributes and can be drag 'n' dropped to change the value.
We can define the min-max values, default value on initial load, color and put it into "read-only" mode (which is also good for using it as a visualization component).
There are no documents for the plugin but things are very straightforward and checking the source code of the demo is pretty enough to learn its logic.
Compatibility: All Major Browsers