40 CFR § 1065.790 - Mass standards.

(a) PM balance calibration weights. Use PM balance calibration weights that are certified as NIST-traceable within ±0.1% uncertainty. Make sure your highest calibration weight has no more than ten times the mass of an unused PM-sample medium.

(b) Dynamometer, fuel mass scale, and DEF mass scale calibration weights. Use dynamometer and mass scale calibration weights that are certified as NIST-traceable within ±0.1% uncertainty.

[88 FR 4687, Jan. 24, 2023]