Commercial invoices and product specifications should clearly state whether the clock operates on battery, AC power, or both. Technical datasheets from the manufacturer that confirm the power supply type are the most reliable supporting documents and can expedite customs clearance.

The movement type — clock versus watch — is determined by technical criteria in the schedule notes, typically relating to movement size and construction. Wall clocks almost always contain clock movements, but if a miniature or novelty wall clock houses a movement meeting watch-movement criteria, it would be classified differently. Verification against schedule definitions is advisable for unusual articles.