26 U.S.C. § 5204: Gauging

The Secretary may by regulations require the gauging of distilled spirits for such purposes, as he may deem necessary, and all required gauges shall be made at such times and under such conditions as he may by regulations prescribe. For the determination of tax and the pre­vention and detection of frauds, the Secretary may prescribe for use such hydrometers, saccharometers, weighing and gauging instruments, or other means or methods for ascertaining the quantity, gravity, and producing capacity of any mash, wort, or beer used, or to be used, in the production of distilled spirits, and the strength and quantity of spirits subject to tax, as he may deem necessary; and he may prescribe regulations to secure a uniform and correct system of inspection, weighing, marking, and gauging of spirits. The Secretary may by regulations require the proprietor of a distilled spirits plant, at the proprietor’s expense and under such supervision as the Secretary may require, to do such gauging, marking, and branding and such mechanical labor pertaining thereto as the Secretary deems proper and determines may be done without danger to the revenue.