The nefarious Major Uncertainty has kidnapped Monsieur Kilogram, putting the world’s measurements of mass in jeopardy. As the world spirals into “Mass Hysteria,” the remaining SI Superheroes, champions of the metric system, leap into action to save the day, and hopefully Monsieur Kilogram as well.

This crisis kicks off the third and latest adventure from the League of SI Superheroes, the animated online series from the National Institute of Standards and Technology (NIST). “Mass Hysteria” touches upon a topic—how to redefine the basic unit of mass known as the kilogram—that represents a cutting-edge undertaking for researchers working to modernize the worldwide metric measurement system known as the International System of Units (SI).

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