Example 2 of Allocation by Mass In this example, the output is Sodium Hydroxide (NaOH) (52.3%), Chlorine (CL) (46.4%), and Hydrogen (H2) (1.3%). The main product is Sodium Hydroxide, and the other two are co-coproducts. In such a case, Allocation by mass or price can be performed among the product and the co-products. System Expansion: What is it exactly?