27 C.F.R. § 19.611 – Records of tax determination in general.

(a) Taxable withdrawals. Except as otherwise provided in this part, a proprietor must gauge and determine the tax on spirits when they are withdrawn from bond. When spirits are withdrawn from bond, the proprietor must also prepare a record of the tax determination in accordance with paragraph (b) of this section.
(b) Form of record. A serially numbered invoice or shipping document, signed or initialed by an agent or employee of the proprietor, will constitute the record of tax determination. Although neither the proof gallons nor the effective tax rate must be shown on the record of tax determination, each invoice or shipping document must contain information sufficient to enable TTB officers to determine the total proof gallons and, if applicable, each effective tax rate and the proof gallons removed at each effective tax rate. For purposes of this part, the total proof gallons calculated from each invoice or shipping document constitutes a single withdrawal.
(26 U.S.C. 5207)