27 CFR 19.353: Bottling tank gauge.

When a distilled spirits product is to be bottled or packaged, the proprietor must gauge the product after any filtering, reduction, or other treatment, and before bottling or packaging begins. The gauge must be made at labeling or package marking proof, subject to variations in accordance with the tolerances set forth in § 19.356(c); however, the actual measurement of the gauge must be entered on the bottling and packaging record required in § 19.599.