From the earliest civilizations through the discovery of the Higgs boson, measurement of the quantity now known as "mass" has always been important; contemporary mass measurements are required for commerce, technology, and even tests of fundamental physics. Reliable measurements of mass and its "related quantities" which include force, pressure, hardness and density of materials, viscosity of liquids, the flow of liquids and gases through pipelines and other conduits, and the gravitational acceleration on the Earth's surface underpin measurement results in many diverse areas. At the highest level of accuracy, these activities require the collaboration of National Metrology Institutes whose experts participate in the specialized working groups of the Consultative Committee for Mass and Related Quantities (CCM). Much of their work involves "key comparisons" designed to test the principal techniques of each field and to help assess participants' measurement capabilities.
At present, a significant CCM activity focuses on the unit of mass, the kilogram. Since 1889, this unit has been defined as the mass of a unique object known as the "international prototype of the kilogram". It is simply a cylinder of platinum alloy stored at the BIPM and, to conserve its mass, used only rarely.
Research shows that it is now practical to define the kilogram in terms of the constants of physics, which by their nature are invariant and universally accessible. In 2011 the General Conference on Weights and Measures (CGPM) endorsed this approach and set out the final steps needed before redefinition of the kilogram (and three other units) can occur. In 2014 the CGPM encouraged the International Committee for Weights and Measures (CIPM) and all other parties involved to complete all work necessary for an adoption of the revised SI at the 26th meeting of the CGPM (2018). It is now the task of the CCM to help coordinate diverse experimental efforts aimed at redefining the kilogram, to test various methods that will realize and disseminate the redefined kilogram, to integrate the new definition seamlessly into familiar quality-control systems used by industry and science, and to explain these changes to user communities. The CCM work is following a roadmap that achieves these goals in 2018.