27 C.F.R. § 25.42 – Testing of measuring devices.

(a) General requirements. If a measuring device such as a meter or gauge glass is used to measure beer, the brewer shall periodically test the measuring device and adjust or repair it, if necessary. The brewer shall keep records of tests available for inspection by appropriate TTB officers. Records of tests will include:
1. (1) Date of test;
2. (2) Identity of meter or measuring device;
3. (3) Result of test; and
4. (4) Corrective action taken, if necessary.
(b) Requirements for beer meters. The allowable variation for beer meters as established by testing may not exceed ±0.5 percent. If a meter test discloses an error in excess of the allowable variation, the brewer shall immediately adjust or repair the meter. Adjustments will reduce the error to as near zero as practicable.
(c) Authority to require tests. If the appropriate TTB officer has reason to believe that the accuracy or reliability of a measuring device is not being properly maintained, he or she may require the brewer to test the measuring device and, if necessary, adjust or repair the measuring device.
(Sec. 201, Pub. L. 85-859, 72 Stat. 1395, as amended (26 U.S.C. 5552))