For nearly 130 years, the world’s scientists have used a singular small, metal cylinder to define the exact weight of a kilogram. But that is about to change. The cylinder was made in 1889 of platinum and iridium metals. It is called the Grand K. The International Bureau of Weights and Measures, or BIPM, keeps the object at its headquarters near Paris. Many safeguards protect the Grand K. In fact, it takes three specially chosen people to open the container that holds the cylinder. They must each release separate locks at exactly the same time to do so. The Grand K has served as the official world measurement tool for weight in kilograms. All modern mass measurements have been based on the Grand K. There are seven main units of official measure.