http://afone.as.arizona.edu/~cary/fnjm/a_diff.porthole.gif
http://afone.as.arizona.edu/~cary/fnjm/a_diff.whiskers.gif
http://afone.as.arizona.edu/~cary/fnjm/a_diffnme.gif
http://afone.as.arizona.edu/~cary/fnjm/diffidence.gif