Adding an External Reference to a Diagram
To add an external reference to a diagram:
1. In the diagram object inserting bar, click
External reference 
.

To add
External reference to the insert bar: in the diagram toolbar, click
Views and details 
and select
External references.
2. Click in the diagram.
The Add External reference box appears.
3. In the Name field, click the arrow and select the (already existing) externel reference of your choice.
4. Select the external reference and click OK.
The name of the external reference appears in the Add External Reference window.
5. Click Add.
The external reference is added to the diagram.