The International Bureau of Weights and Measures was founded in 1875 to answer a question that had troubled humanity since the beginning of civilization: How do we accurately measure something? Take mass, or the amount of matter in an object, for example.
For much of history, people relied on simple balance scales to compare the mass of one object to another. If the masses on either end of the scale were unequal, the scale would be out of balance. If the masses were roughly the same, the scale would be even.
But to determine an object’s exact mass, you need an agreed-upon unit of measure. Some societies used pieces of grain or objects called weighing stones. But having different standards of measurement in different places made trade difficult. So in 1799, a group of French scientists developed a solution: the metric system.
The unit of measure for mass became the kilogram, which was based on the mass of a liter of water at a certain temperature. In 1889, the International Prototype of the Kilogram, nicknamed the Grand K, was commissioned. The weight was made of a corrosion-resistant alloy, a metal mixture that contained 90 percent platinum (Pt) and 10 percent iridium (Ir). It would be the unit of measure “for all people, for all time”—or so metrologists thought.