Code of Federal Regulations Title 40. Protection of Environment § 40.1065.790 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.