It’s a conundrum scientists need to solve because the kilogram is one of a few base units (like the second and the meter) that are used in the definitions of other, more complex units, such as those used to measure temperature, electricity or density. If the kilogram is off, even a little, critical measurements in science, engineering and commerce get messed up.[...]
The U.S. National Institute of Standards and Technology is backing a definition based on the Planck Constant, a number from quantum mechanics. It’s a more complex definition than a simple cylinder, but it’s unlikely to change over the next century.
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