update the readme with more information about the deltas

Author: brandonaaron

README.md

@@ -30,6 +30,24 @@ The old behavior of adding three arguments (`delta`, `deltaX`, and `deltaY`) to
 event handler is now deprecated and will be removed in later releases.
 
 
+## The Deltas...
+
+The combination of Browsers, Operating Systems, and Devices offer a huge range of possible delta values. In fact if the user
+uses a trackpad and then a physical mouse wheel the delta values can differ wildly. This plugin normalizes those
+values so you get a whole number starting at +-1 and going up in increments of +-1 according to the force or
+acceleration that is used. This number has the potential to be in the thousands depending on the device.
+Check out some of the data collected from users [here](http://mousewheeldatacollector.herokuapp.com/).
+
+### Getting the scroll distance
+
+In some use-cases we prefer to have the normalized delta but in others we want to know how far the browser should
+scroll based on the users input. This can be done by multiplying the `deltaFactor` by the `deltaX` or `deltaY`
+event property to find the scroll distance the browser reported.
+
+The `deltaFactor` property was added to the event object in 3.1.5 so that the actual reported delta value can be
+extracted. This is a non-standard property.
+
+
 ## See it in action
 [See the tests on Github](http://brandonaaron.github.io/jquery-mousewheel/test).