By-jove I've got it! We need a chart, all the person has to do is input the numbers, in any order, press go, the software plots the lines for everyone against the index chart, the closest wins?
Just post a single chart each week, a splash of colour to make it pretty, all automated, 3 monthly calculation with usual weekly input, Amazon voucher on the way...
Is there a free charting platform that could enable collaborative competitive trading, we could input our own weekly numbers and show the results, job done?