Hi Hajer,
It all depends on the properties of the keyfigure you define and the calculations you perform on them. You are the best one to find the point of problem as it is not a common problem to say a solution. It is just a guess we can give you..
Check your Keyfigure how you defined and the properties of it. and check the data as well. You will surely get your solution.
Regards
Deva