If you are assessing the scatter of wheels, and can’t seem to find one with above a 70% rating, see the updated information at http://www.roulettephysics.com/forum/index.php?action=kb;area=article;cont=56 (you need to be logged into the forum).
In some cases, you may be getting a rating worse than it should be. The updated knowledgebase article explains alternate methods for scatter analysis. They are slightly more difficult, but give you a more realistic idea of how predictable the ball bounce really is.