Repeating screens with total updates

Hello -

I am trying to have a Medialab (v2008) program play a trading game with a participant. As such, the response is calculated based on what the participant does. I want to play over 100 rounds, and I was trying to not have to enter those each as separate screens. The problem is how to keep my variables up-to-date. For example, I have a point total that I want to display on each screen and this is based on the collective points from the previous rounds. If I put a totalpoints variable in responses.xml the only way I know to have it calculate the total that will be correct until the end is to sum all the rounds. Unfortunately this won't equal zero when the program begins as every choice the participant makes earns some amount of points. I need a way to keep a running point total - variables that I can update and override as the program continues. I have tried naming the variable the same in hopes that it would override the previous making a loop of sorts. It gives me an error. The only way I can think to do save variables and update them is through a HTML/Jscript custom call with cookies, but with that I don't know how to get the information back into Medialab. I'd appreciate any ideas.

Daniel