Formula in a Matrix

Hi all,

I have a matrix with product and its category as rows and sales, volume and unit price as columns.

we have a difficulty in showing the unit price when drill up/down as the following picture.

We want to show the price even when drill up/down.

The core problem is that 'unit price' differs from 'sales' and 'volume' in its nature

in that it can't be summed up.

One of my ideas is if we can write a formula in the matrix just like Excel so that

'unit price' column is calculated based on 'sales' and 'volume' whenever it is
drilled up or down, but I don't have any idea to realize this.

Any idea or suggestion are welcome.

Thanks, Shinya