Evolution of the International System of Units: considering the challenge of user adoption

This discussion considers the challenge of making amendments to the International System of Units (SI) in terms of the varying levels of adoption of these amendments by users of the SI. It categorises possible amendments along two scales. First, whether these are changes or additions to the SI; and second whether these amendments are optional or compulsory. Where amendments fall on these two scales gives an indication of whether they are low-risk or high-risk actions, in terms of their likely adoption by users of the SI and the confusion that lack of adoption might cause. Proposed amendments to the SI of current interest are considered with respect to this framework.