AX SSRS chart series value variance needed

Hi,

I am working on a AX 2009 SSRS report to show the number of projects started per month for this year and last year.

My problem is how to show the varaince between last year and this year, per month(an adjacent column per month).

Value:      =Count(Fields!Project.value)

Categoey: =Fields!Month.Value

Series:      =Fields!Year.Value

Can anyone suggest on this.