How to have cumulative value calculation

Hi All

Below is my report in which i need to find cumulative value 

i am using code =RunningValue(CInt(Fields!Variance.Value), Sum, Nothing)

but the result comes as -10 ,-25,and so on for the 1st row 

and -459,-474 for the second row

I just need cumulative to be to calculate to 1st row and 2nd row it needs to start fresh

for e.g 2nd row it should be -10,-35 and so on

Any help on this much appreciated

Thanks

Pradnya07