Revamping the metric measure of mass
Precise count of Avogadro’s number furthers efforts to redefine kilogram
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2015/07/ss_kilogram_free.jpg?fit=860%2C460&ssl=1)
MEASURING UP This metal cylinder is the United States’ copy of the international kilogram kept in France. Scientists hope to replace this standard, the last physical object used to define a unit of the metric system, with a definition of mass based upon fundamental physical constants.
Robert Rathe/NIST/Flickr