A device designed in one country, built from components made in four others and assembled in a sixth must still declare a single country of origin at a border. That declaration is a legal conclusion rather than a description.
Origin determines what is owed at the border
Tariff rates, quotas, trade remedies and preferential treatment under trade agreements all depend on origin.
The same physical product can face very different duties depending on which country it is deemed to come from, which makes the determination financially significant.
Labelling requirements for consumers are a separate question with separate rules, and the two answers do not always match.
Substantial transformation is the general test
The common standard asks where the product last underwent a change that gave it a new name, character or use.
Cutting fabric and sewing it into a garment is normally transformative. Putting a finished product into a retail box is not.
The difficulty is that most manufacturing sits between those poles, and the answer depends on how much of the product's essential character was created by each step.
Trade agreements use their own arithmetic
Preferential agreements typically replace the general test with specific rules for each product category.
These may require a change in tariff classification, meaning the inputs and the output fall under different customs codes, or a minimum share of regional content by value.
Automotive rules go further still, setting content thresholds for particular components and, in some agreements, labour value requirements.
Assembly is a weak signal on its own
Because assembly can be moved easily, rules are written so that final assembly alone does not confer origin when the substance of the product was made elsewhere.
Customs authorities examine where the value was added, what processes were performed and whether the operation had a purpose beyond changing the declared origin.
Operations that exist mainly to alter a tariff outcome are treated as evasion rather than as manufacturing.
Companies seek certainty in advance
Because the determination is technical and expensive to get wrong, importers request binding rulings from customs authorities before shipping.
A ruling describes the product and the process and states which country the goods will be treated as coming from, which the importer can then rely on.
Origin engineering, meaning designing a supply chain around these rules, is now a routine part of sourcing decisions, and it is why production shifts sometimes follow rule changes rather than cost changes.