XYZ analysis: how?

[#1]

Hi!

I have table with fields:

Date

Product

Cost

I want to develop XYZ analisys by Product.

Time unit is MONTH.

In XYZ there is formula:

SUM (sqr ( AVGbyMonth (CostOfProduct) - AVG  (CostOfProduct))).

How I can get the AVGbyMonth (CostOfProduct)?

I tried to generate calendar and join my table and calendar table (field Month) - my computer is 100% busy for ling time (I think, I do something wrong).

Please help me!

And if you can share to me your examples of XYZ analysis - do it please.

Thank you!