jQuery UI Sortable, how to determine current location and new location in update event?

I have:

<ul id="sortableList">
     <li>item 1</li>
     <li>item 2</li>
     <li>item 3</li>
</ul>

I have wired into the update: function(event, ui) { } but am not sure how to get the original and new position of the element. If i move item 3 to be above item 1, I want the original position to be 2 (0 based index) and the new position of item 3 to be 0.