(Sorry, I put this comment on the original commit, but pasting it here to explain the rationale:)

I left the simplified one commented out since I wasn't sure which version we'd prefer. There are different default behaviors on certain OS+browser+device+configuration combinations that might scale the "delta" value of a mousewheel event based on acceleration, or just return a different value than most other browsers. (See [here](https://developer.mozilla.org/en/docs/DOM/DOM_event_reference/mousewheel) and [here](http://stackoverflow.com/q/5527601/357774).) As you can see, the current uncommented version is not *completely* normalized (which may be impossible).

The simplified version follows the following logic: one mousewheel event => one step scrolled on the chart in the appropriate direction.

It's debatable as to whether the current, scaled version enhances the user experience for a certain small percentage of users, but please let me know your opinion as to which version you think we should keep.