--- a/proposals/mousewheel.txt	Tue Oct 23 16:01:48 2007 +0900
+++ b/proposals/mousewheel.txt	Tue Nov 06 01:38:58 2007 +0900
@@ -65,13 +65,19 @@
 };
 
 If the <code>mousewheel</code> event is cancelled, only the default action for
-vertical wheeling is cancelled. The wheelDelta attribute is a number indicating
-the distance (positive means rotated away from the user, negative means rotated
-towards the user). The default value of the wheelDelta attribute is 0.
+vertical wheeling is cancelled. 
+
+    wheelDelta
+        A number indicating the distance, measured as the number of "clicks" the wheel has been rotated. A positive value indicates that the wheel has been rotated away from the user (or in a right-hand manner on horizontally aligned devices) and a negative value indicates that the wheel has been rotated towards the user (or in a left-hand manner on horizontally aligned devices). The default value of the wheelDelta attribute is 0.
+
+        A "click" is defined to be a unit of rotation. On some devices this is a finite physical step. On devices with smooth rotation, a "click" becomes the smallest measurable amount of rotation.
+
 
 XXX: What about UIEvent.detail?
 
 For both <code>mouseomniwheel</code> and <code>mousewheel</code>,
 <code>MouseEvent.relatedNode</code> must indicate the element over which the
 pointer is located, or <code>null</code> if there is no such element (in the
-case where the device does not have a pointer, but does have a wheel).
\ No newline at end of file
+case where the device does not have a pointer, but does have a wheel).
+
+