in reality phil, it means that anything one side of half way is lean (usually left by convention) and other other side of half way is rich, which is why it looks like it flies around so much.. at WOT on boost I'd expect it to show steady rich fairly much up one end, depending on the LED display characteristic. Quite likely they may all go off completely at the other end when you lift off.
It is possible to expand the middle part of the display characteristic in the electronics to give a more "linear" look to the way the LED's light up, but it's contrived really unless it's specifically calibrated to the individual sensor example and the temperature of the sensor is controlled.