and with such conditions as the Secretary determines necessary to ensure payment of the fees imposed under this section. (c) Measurement of imported products The amount of any covered product which is imported into the United States shall be determined by the measure ordinarily used in the course of trade of such covered product (as determined pursuant to the 6-digit HTS subheading number with respect to such product). (d) Amounts and fees The Commissioner of U.S. Customs and Border Protection shall allow payment of the fee imposed under this section for such product to be paid by the covered entity in the same manner in which payment of custom duties are made. 4692. Determination of variable charge (a) In general The variable charge is an ad valorem fee which is specific to a covered product and determined pursuant to the tier to which such covered product is assigned. (b) Tiers (1) In general Tiers for covered products shall be established as follows: (A) For covered products for which the pollution intensity difference is greater than 10 percent and not greater than 50 percent, tiers shall be established at each 5-percentage-point increment. (B) For covered products for which the pollution intensity difference is greater than 50 percent and not greater than 200 percent, tiers shall be established at each 10-percentage-point increment. (C) For covered products for which the pollution intensity difference is greater than 200 percent, tiers shall be established at each 20-percentage-point increment. (2) Application of tiers (A) In general The purposes of the tiers under this section are as follows: (i) To provide for a standardized organization model for each covered product to allow for proper implementation and application of the fee imposed under section 4691, with such tiers to be based on the different pollution intensities for a given covered product based on the country of origin of such covered product (or, subject to section 204 of the Foreign Pollution Fee Act of 2023 , the manufacturer of such covered