19 CFR § 146.94 - Records concerning establishment of manufacturing period.
(a) Feedstock admitted into the refinery subzone. The operator must maintain appropriate inventory records during the manufacturing period to substantiate the feedstock(s) eligible for attribution under § 146.93(b) and in accordance with the operator's selected attribution method.
(c) Consumption or removal. The consumption or removal of a final product during a week may be considered to have occurred on the last day of that week for purposes of attribution and relative value calculation instead of the actual day on which the removal or consumption occurred, unless the refiner elects to attribute using the FIFO method (see section II of the appendix to this part).
(d) Gain or loss. A gain or loss that occurs during a manufacturing period must be taken into account in determining the attribution of a final product to a feedstock and the relative value calculation of privileged foreign feedstocks. Any gain in a final product attributed to a non-privileged foreign status feedstock is dutiable if entered for consumption unless otherwise exempt from duty.
(e) Determining gain or loss; acceptable methods -
(1) Converting volume to weight. Volume measurements may be converted to weight measurements using American Petroleum Institute conversion factors to account for gain or loss.
(2) Calculating feedstock factor to account for volume gain or loss. A feedstock factor may be calculated by dividing the value per barrel of production per product category by the quotient of the total value of production divided by all feedstock consumed. This factor would be applied to a finished product that has been attributed to a feedstock to account for volume gain.
(3) Calculating volume difference. Volume difference may be determined by comparing the amount of feedstocks introduced for a given period with the amount of final products produced during the period, and then assigning the volume change to each final product proportionately.