Price/volume effects by customer groups

[matcoq]

Hello

I need to calculate price / volume / mix effects between year N and N+1, but by customer groups. So by customer it is very easy to have each effect:

• Price = (Price N+1 - Price N) * Volume N
• Volume = (Volume N+1 - Volume N) * Price N
• Mix = (Price N+1 - Price N) * (Volume N+1 - Volume N)

However when I try to roll up by customer groups (with average selling prices that are weighted, by definition) the total impact is correct but the split is not, and also thetotal is not equal to the sum of rows... (see red values in my table, rows 12/21/31)

I have posted the file here : https://docs.google.com/spreadsheets/d/12kutrY0-vK9JBrvmrfV06gThYQhJTFGOWUEXKklaIKI/edit?usp=sharing

Thanks a lot in advance!