TS has more then one positive rating, he has 12 positives. That scenario is not addressed above.
I think it is addressed above or am I wrong? No matter how many positive feedback you get *before* negative feedback, rating will be ???. The next positive feedback negates it and make rating 0. Please correct me if I am wrong.
-snip-
else
score = unique_positive - 2^(unique_negative)
if score >= 0
start_time = time of first negative
score = unique_positive since start_time - unique_negative since start_time
P.S.
There is no decay. Ratings grow in weight from 1 to 10, then stay at 10 forever. (If the rated person has no negatives.)