On the purchase order line, tab Foreign trade there is a field called Unit weight. The description of the field says:
The unit weight of the selected item. For transaction lines that are identified by a product, the information in this field comes from the item record and is not editable. For transaction lines that are identified by a description, you can enter the unit weight.

We have those items that are generic, where the weight is different from time to time. But where do I set up that a transaction line should be identified by a description? I need it to be editable.
BR
Anette