Abstract: A system for controlling the flow of semiconductor products and their components through a production facility including assembly and final testing of a large number of different products with multiple product grades. The system stores information on the demand and inventory of all product grades together with grade distribution data giving the yield of all co-products of a product family from testing the common component of that family. The system includes means for calculating the number of common components to be tested to cover the requirements for all co-products of a family. The distribution data also gives the yield of all by-products of a test for particular products, and the system operates to adjust the inventory status for other products corresponding to such by-products, to avoid excess production of such other products in meeting projected demand.