Adrien-Marie Legendre (1752–1833) was a brilliant French mathematician and physicist. He is known for his studies of ellipsoids (leading to what we now call the Legendre functions) and celestial mechanics, and he worked on the orbits of comets. In 1787 he helped measure the Earth using a triangulation survey between the Paris and Greenwich observatories. In 1794 Legendre published *Eléments de géométrie,* an elementary text on geometry that would essentially replace Euclid’s *Elements* and would remain the leading text on the topic for close to a century. Finally, Legendre also had a connection to measurement: In 1791 he was appointed to the committee of the Académie des Sciences, which was assigned the task of standardizing weights and measures.

Rulers in the United States commonly show length measurements in both metric and English units.