Samples taken in accordance with § 151.52 shall be promptly forwarded to the appropriate Customs laboratory for testing in accordance with commercial methods. An authorized CBP official may secure from the importer a certified copy of the commercial settlement tests for moisture and for assay which shall be transmitted with the commercial samples to the Custom laboratory. If the Customs tests are not in substantial agreement with the settlement tests, the Customs laboratory director shall review his tests. The Customs tests shall be used in determining the final duties on the merchandise, except that the settlement tests shall be used if, in the opinion of the Customs laboratory director:
(a) The settlement and Customs tests differ by no more than is to be expected between qualified laboratories, and
(b) The use of the settlement test results will not require a different tariff classification or rate of duty than is indicated by the Customs test.