Crystal Reports Progression summary

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     hi,

  i am new to the forum. i am using cr 8.5+vb. i have a problem. i am making a report where i have to make sum with the prevous value.
say the values are

                  4
                   5
                   2

in my summation column 1 st row eill be 4 , second row will be(5+4)=9
and the third will be (9+2)=11.

i have i will get my answer from this forum.

thanks in advance.

                                                            calcu