Me. Rev. Stat. tit. 10, § 2352

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 Bureau of Standards, or its successor organization, the National Institute of Standards and Technology, shall be the state primary standards of weights and measures and shall be maintained in such calibration as prescribed by the National Bureau of Standards or the National Institute of Standards and Technology, as applicable. All secondary standards may be prescribed by the state sealer and shall be verified upon their initial receipt and as often thereafter as determined necessary by the state sealer.