The metric system of measurement, more correctly called the International System of Units, is a system of weights and measures agreed through a network of international agreements. Using the first two initials of its French name Système International d'Unités, the International System is called SI. The foundation of the system was laid out in the Treaty of the Meter (Convention du Mètre), signed in Paris on May 20, 1875. The United States was a founding member of this metric club, having signed the original document in 1875. Forty-eight nations have signed this treaty, including all of the major industrialized countries.

The Bureau International des Poids et Mesures (BIPM) is a small agency in Paris that supervises the SI units. The units are updated every few years by the Conférence Générale des Poids et Mesures (CGPM), which is attended by...