Compute the circumference using the size of the largest title, so that they'll all fit.
Convert to using bounds and position.
Convert to use layoutSubviews. Call setNeedsLayout() when appropriate in view controllers.
#19: Some improvement on resizing. Not well tested. (The demos don't resize the knobs.)
Support Dynamic Type changes in the Obj-C demo. (And make sure not to blow up on iOS 6.)