Comment by mattmanser

Could do with some smoothing and polishing. Jerks all over the place.

Also, what is with this new fashion of declaring functions as anonymous methods?

    var recalculateLimits = function () { 
       /* snip */
    }; 
    var update = function () { recalculateLimits(); onScroll(); };

Have I missed a memo?

EDIT: I forgot to say apart from my moaning, does the job, good code, good job! And it's only jerky when you use the scroll button on a mouse.