Variable values in a measure

Hi,

I would like to use a something like a variable measure based on values I select. 

I have 4 tables (Alpha, Bravo, Charlie, Delta) like this: 

each containing stock number of certain product and its sales.

Combined in a table like this:

Last column is a measure dividing all inventories (Inventory of Alpha, Bravo, Charlie and Delta) by all sales. But I would like to be able to select which of the inventories are going to be divided by which of the sales. 

In the example above I would like the Dividing measure to show a value calculated like (Alpha Inv + Charlie Inv) / (Bravo Sales + Charlie Sales + Delta Sales). 

I don't want to use Filed parameters with predefined combinations since in my model there are many categories like Alpha, Bravo etc.

In an ideal scenario I would like the table to always show all of the inventory and sales categories (columns) but just the measure would be calculated based of a selection of inventory and sales groups.

Here is the sample file: File 

Any help would be greatly appreciated.