What does the Fisheye Image Enclosing slide bar do (In PW4)?  It's not mentioned in the documentation. I understand the concept of enclosing the image inside the yellow circle, and using the Center X, Y and Radius to adjust the circle, but I've not figured out what the slide bar is for.  It seems to auto-fit the circle, but the number that it's on doesnt make any sense. 

Is that like 100 presets and you can use the bar to select from any of them? 

Thanks!

~shawn