The FAQ section on the home page has this info.
http://www.contour.org/FAQ/FAQ.cgi?s=probs&display=checkengine Sensor 21 is bank 2 upstream, bank 2 is the front bank (i.e., next to rad).
p.s. I have a 1st, 2nd and 3rd-born, so if you don't mind I'll pass, on the reward.
