10 Week Countdown 2010

[non-gravity]

( (predicted - real)/real*100% plus (predicted - real)/predicted*100% )/2

and then taking the absolute number in whole points .

 

example:

Predicted 200 Real sales number 250

( (200-250)/250*100 plus (200-250)/200*100 )/2 = -22,5 = 23 points