Paretto

Hi! i have the following problem.. i have a mesaure that indicate the units sold and i have to do a paretto. i have to create another mesaure that acumulate the units to do a paretto.
Ex:
Units-Acumulative
3---------3
5---------8
6---------14

How can i do this with a calculated member?


thank´s
Paul

Ok, i´ve resolved the problem in that way:
Sum(Head(Order ( {[Centro de Costo].Siblings}, [Measures].[Importe], BDESC) AS OrderedSiblings, RANK( [Centro de Costo], OrderedSiblings )) , [Measures].[Importe])

Tks
Paul