It is possible to link production units to represent upstream and downstream relationships between them. On the production unit page, you can add both upstream and downstream links på pressing the Edit button:

When pressing Edit, there are buttons to remove and add both suppliers and up- and downstream production units:

Production unit tiers

By linking production units together, you represent the flow of materials through the supply chain. If you want to have a more visible labeling of which production units act as tier 1, tier 2 etc, we recommend adding tier as a property on the production unit directly. 

Many companies apply different policies and processes depending on tier information, and the links described here are not the best way of representing tiers, because one vertically integrated factory might act as both tier 2 and tier 3. 

By having the tier information as a property on the production unit rather than derived through the links to others, it will be possible to mark this production unit as both tier 2 and tier 3.

Permissions

Users will be allowed to link production units if the have the Link permission set on their user role.