Custody-transfer meters are used at points where ownership of a liquid commodity — crude oil, refined products, LNG — changes hands, and they must meet stringent accuracy standards (typically API MPMS or OIML R117) with documented calibration traceability. General-purpose flow meters used for process monitoring or internal accounting do not carry the same legal-for-trade requirements. Importers supplying custody-transfer applications should obtain calibration certificates and type-approval documentation from the foreign manufacturer before shipment.

In practice, utility billing meters and industrial process meters are distinct product lines. Utility water meters must meet AWWA standards and receive state weights-and-measures approval for legal-for-trade use; industrial process meters are selected for chemical compatibility, pressure rating, and accuracy class rather than regulatory approval. A meter approved for utility billing can technically be used in a process application, but the reverse is generally not permissible for billing purposes without formal type approval.