Settlement method
When the incentive period ends, every user's answer portfolio is fictitiously "sold" at current market prices. This final valuation is compared to the original amount of credits invested. Note that only trades done during the incentive period are relevant for this valuation, other trades are ignored or reversed automatically.
Advantages and disadvantages
With this method, credit winnings are only possible if other users trade the prices even more towards the real equilibrium. Every trader must leave something on the table for others and has a deep interest to convince others to invest along the same investment idea. Thus the trader will share his thoughts with others and strongly argue their target price.