Delta calculation

[raghunori]

Hello Cognos experts..I have a crosstab visual in Cognos dahsboard which shows opening balance and ending balance month to month. Ideally, ending balance of previous month should be equal to opening balance of current month but we end up getting some delta. So i need to show this delta which is difference between opening balance of current month and ending balance of previous month as shown below. I am struggling with the calculation. can you suggest how to accomplish this?

   Month1   Month2   Month3
         
opening balance   180   203   206
         
ending balance   200   205   

Delta.                        3        1