May 22, 2019
Thank you, Mrs. Leonberger
Tucked away somewhere in the basement of the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, is a precious collection of small metal cylinders that literally define the mass of everything in the United States: the kilogram. The kilogram currently has one very simple definition: It is the mass of a chunk of platinum-iridium alloy that’s been housed...
