[supercat]

So there’s no contract which pays out if the difference is, say, -6.1%?

It would have made things a lot clearer if they were bracketed: "+5 to +100", "+2.5 to +5", "0 to +2.5", "-2.5 to 0", "-5 to -2.5" and "-100 to -5". That would avoid any ambiguity. Still, I find it curious that there's no contract for the last option, since it would be the one most likely to win.

[cmj328]

I think I've finally figured out how to read it. Here are the implied bets based on the current bid prices 3.3, 33.0, 55.0, 66.0 and 80.0.

Difference from final RCP average	=	Implied Bet	How to calculate implied bet
+5 to +100	=	3%	(>5.0 bid price)
+2.5 to +4.999	=	30.3%	(>2.5 bid price - >5.0 bid price)
0 to +2.499	=	21.7%	(>0.0 bid price - >2.5 bid price)
-2.5 to -0.001	=	11%	(>-2.5 bid price - 0.0 bid price)
-5.0 to -2.499	=	14%	(>-5.0 bid price - >-2.5 bid price)
-100 to -5.001	=	20%	(100 - >-5.0 bid price)

I'm guessing you can bet the last bracket by shorting the >-5.0 contract.