calculation base on break on a crosstab. How to?

I build a crosstab table that showes the sales revenue development for each city year over year (Attached is an example from efashion)

I made break on city.

Now at the yellow row at the picture I want to calculate the growth between months year over year

on January for California its should be -- 288,260 / 226,268 - 1 = 27% and so on...

I guess I need to do somthing like this : [sales revenue] where ([year] = 2006) / [sales revenue] where( [year] = 2005) -1

but what if i want it dynmic?

I mean It will always be a comparison between two periods (two rows) the years can changed every time either by input control or by selected diffrent years on the query.

Is it possible?