http://www.jmrware.com/articles/2008/leverlink/LeverLink.html

The Lever Link device adds dramatically improved roll response to a flex wing hang glider by applying the mechanical lever principle to the sideways force placed on the keel which greatly enhances the wing warping rolling moment when a pilot shifts to one side. The sideways roll force placed on the keel can be easily increased many fold (by a factor of 2, 4, 6 or more) and this effect can be progressively applied as a function of sideways displacement. The amplifying effect can be adjusted in a wide variety of ways by varying the Lever Link geometry. This enhanced roll control will make flying hang gliders safer, easier and more enjoyable and will allow small pilots to fly large gliders with ease.