In order to get some volume discounts on a part I will purchase some in a case quantity of 2500 and then some in boxes of 50.

I have setup products before using units of measure but how do you keep track of the same part so it shows a total of the combined orders?

For instance if I order 1 case of 2500 pieces and then 4 boxes of 50 I will have an inventory amount of 2700 pieces of "product x".