A factory produces seven metal rods and measures their lengths (in millimeters) under two different machine settings, A and B. Under setting A the lengths are 12, 15, 18, 20, 22, 24, 30. Under setting B they are 13, 16, 19, 21, 23, 25, 31. To the nearest tenth of a millimeter, how much greater is the median length in setting B than the median length in setting A?
