Left offset positioning within relative positioned parent

Hi, I was experiencing a problem with a position of a pointer when a slider was placed within an element having some margin and relative position (see http://jsfiddle.net/tNmwY/). I've fixed it by adding a parent offset to the slider offset.
Use my fix or throw it away and use some more elegant. I just want to report issue and propose some solution and also thank you for such a useful directive.

Rosta