(a) Gauge of spirits in packages. When determining the quantity of bulk spirits in packages, the proprietor must determine the quantity by weight as provided in part 30 of this chapter.
(b) Bulk gauge for tax determination. When determining the quantity of bulk spirits for determination of tax or when performing a production gauge that will be used for tax determination, the proprietor must determine the quantity by weight as provided in part 30 of this chapter or by an accurate mass flow meter. For tax determination purposes, an accurate mass flow meter is a mass flow meter that has been certified by the manufacturer or other qualified person as accurate within a tolerance of plus or minus 0.1 percent.
(c) Volumetric determination. Except as provided in paragraphs (a) and (b) of this section, in all other instances when the proprietor is required to gauge bulk spirits in bond, the proprietor may determine the quantity by either weight or volume. When the proprietor determines the quantity by volume, the proprietor must measure the spirits by using:
(1) A tank or bulk conveyance for which a calibration chart is provided, with the calibration charts certified as accurate by persons qualified to calibrate tanks or bulk conveyances; or
(2) An accurate mass flow meter. For purposes of this paragraph, an accurate mass flow meter is a mass flow meter that has been certified by the manufacturer or other qualified person as accurate within a tolerance of plus or minus 0.5 percent; or
(3) Another device or method approved by the appropriate TTB officer.