That clock, called the Atomic Clock Ensemble in Space, or ACES, launched into orbit from Florida last month, bound for the International Space Station. But it’s of special interest for geodesists because it can be used to make gravitational measurements that will help establish a more precise zero point from which to measure elevation across the world. Alignment over this “zero point” (basically where you stick the end of the tape measure to measure elevation) is important for international collaboration. In 2020, the international height standard even resolved a long-standing dispute between China and Nepal over Mount Everest’s height. ESA-T. PEIGNIERTo create a standard zero point, geodesists create a model of Earth known as a geoid.