Ensuring the stability of primary mass standards during the implementation of the new definition of the kilogram

In November 2018 the General Conference on Weights and Measures (CGPM) will meet and are likely to ratify the revision of the international system of units (SI). This represents a major change to the way the base SI units are defined and realised, a major consequence being that the last of the definitions based on a material artefact, the international prototype of the kilogram, will be "retired" and the "new" kilogram will be realised in terms of the Planck constant via the Kibble balance or X-ray crystal density (XRCD) experiment. While the revision of the SI and the redefinition of the kilogram will almost certainly be endorsed by the CGPM there are issues around the current agreement of the Kibble balance and XRCD experiments. This will mean that in order to implement the kilogram redefinition a consensus value for the "new" kilogram will need to be adopted in order that a consistent value for the SI unit of mass be maintained. In order to maintain this consistency the storage, monitoring and use of current primary mass standards will be critical and this paper outlines ways in which the stability of artefact based mass standards can be optimised by careful storage and monitoring using surface analysis techniques and quartz crystal microbalance technology. (paper)