Calculate rank based on current month vs previous month

[#1]

Greetings

Please help to obtain the desired result for calculating ranks.

I would like to rank the products based on the difference of current month and prior month.

(sum({<product= {"=rank(sum(qty), product<=$(vRank)"}, year = 2016  , month = 2 >}  qty)  )

             -

(sum({<product= {"=rank(sum(qty), product<=$(vRank)"}, year = 2016  , month = 1 >}  qty)  )

Thanks!

[#2]

Many thanks! It's Working.