Mo. Rev. Stat. § 413.045: Calibration of weights and measures as prescribed by the National Institute of Standards and Technology.

Weights and measures that are traceable to the United States prototype standards supplied by the federal government, or approved as being satisfactory by the National Institute of Standards and Technology, shall be this state's primary standards of weights and measures, and shall be maintained in such calibration as prescribed by the National Institute of Standards and Technology. All secondary standards may be prescribed by the director and shall be verified upon their initial receipt and as often thereafter as deemed necessary by the director.