Mass stability of 1-kg stainless steel weights in the past 13 years

As a national metrology institute, the National Metrology Institute of Japan (NMIJ), AIST has been maintaining a group of 1-kg stainless steel weights since 1995. The mass values of the 1-kg weights are referred to calibrate the standard weight sets from 1 mg to 5000 kg aiming at improving the mass standards. Calibrations of 28 pieces of 1-kg weights which made of austenitic stainless steel of non-magnetism, are of a single-piece type with no adjusting cavity have been performed. The reference mass standards are two 1-kg stainless steel weights, being traceable to the international prototype of the kilogram. This paper reports the mass stability of a group of 1-kg stainless steel weights in the past 13 years, and gives a description of the mass comparison procedure using an automatic mass comparator.