Work of David Lewis :His website !!
A message of him on the ATM-list of July 2, 1998
Richard Schwartz sent me some sketches of various cells, including the 4 point cell. According to my program, the best 4 point cell has supports at relative radius .509, and has about half the error of a 3 point cell. I haven't put this on my web site yet, though, so don't look there!