This document amends the Customs Regulations on an interim basis to provide the method for calculating manufacturing substitution drawback where imported merchandise, which is dutiable on its value, contains a chemical element and amounts of that chemical element are used in the manufacture or production of articles which are either exported or destroyed under Customs supervision. Recent court decisions have held that a chemical element that is contained in an imported material that is subject to an ad valorem rate of duty may be designated as same kind and quality merchandise for drawback purposes. This amendment provides the method by which the duty attributable to the chemical element can be apportioned. This amendment requires a drawback claimant, where applicable, to make this apportionment calculation.