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. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your highest calibration weight has no greater 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. Calibration weights may be certified by any calibration lab that maintains NIST-traceability.

[70 FR 40516, July 13, 2005, as amended at 76 FR 57467, Sept. 15, 2011; 86 FR 34574, June 29, 2021]