Consider the following example for the layer of goods:
Goods contain substances! The shown flows of goods may consist of the following substances:
Flow 1: , Flow 2: , Flow 3:
Explanation: e.g. Flow 1 consists of 60 mass units. 10 of them can be allocated to the green substance, 15 to the red. All other substances are displayed white because they are not of interest.
Within a process substances can be split in a different ratio than the goods they are contained in (accumulation, elimination). If the concentration of a substance in a good is known the mass flows of this substance can be calculated easily (here counting the green or red squares respectively).
In this example all particles of the red substance of flow 1 are accumulated in flow 2 (a raise in concentration).
Most of the green substances (but not all) are directed to flow 3.