This can be used in many applications the most popular of which is to use it as a UI slider or knob.
The first step is to create the document, if you want to follow me exactly here's what I began with.
The next step is to get out your Elliptical Marquee tool and draw a circle in the center of the document. I find that the easiest way to do so is by holding Option and Shift and pull from the center toward one corner. It should have about a 600px diameter. It is essential that your circle is exactly in...
