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Every clock on Earth is flawed. Even science’s most accurate atomic clocks are beholden to our planet’s gravitational pull, and end up slowing down ever so slightly over time. That’s why researchers from Shanghai decided to send one up into space.

On Sept. 15, Chinese researchers launched a cold atomic clock into orbit around Earth, where it will only slow down by one second every billion years, as opposed to every 300 million years like the current gold-standard of atomic clocks. The Cold Atomic Clock in Space (Cacs), as it is called, will likely become humanity’s most accurate timekeeping device.

Atomic clocks are largely used for calibrating extremely sensitive electronics, like global positioning systems (GPS), or conducting experiments in hyper accuracy-dependent disciplines like particle physics and geology. According to the South China Morning Post, the Chinese government intends to use Cacs to improve their own national GPS, which currently operates at levels below the system employed by the US.

Atomic clocks were originally created to run on the exact measure of a second as agreed upon by the entire scientific community. Seconds used to be measured as a tiny fraction of a day. The trouble is, the average day includes a lot of variation, depending on where you are and the earth’s axial wobble, caused by its magnetic poles and, more recently, melting ice sheets.

Scientists realized that the way that electrons (the tiny negatively charged particles that surround atoms) jump back and forth between different energy states in molecules or atoms, was a much more precise way of calculating a second. These oscillations end up appearing like vibrations that occur at a constant rate—as long as molecules or atoms are at a constant temperature. Since 1967, the official definition of a second has been “9,192,631,770 vibrations of a cesium 133 atom.”

Laser-cooled “cold” atomic clocks are generally considered to be the most accurate clocks that exist—other clocks and watches, like the kind anyone could buy in a store, tend to slow down over time. Although it’s often just a couple of seconds, that inconsistency won’t do in a research setting.

But alas, on Earth, even cold atomic clocks are prone to slowing down ever so slightly. Because of the force Earth’s gravity applies to atoms, the National Institute of Standards and Technology’s NIST-F2 atomic clock in Boulder, Colorado will slow down by a second every 300 million years.

Cacs, which will orbit our planet gravity-free, will use rubidium atom vibrations to keep time, and will slow down much more slowly than Earth-bound atomic clocks. It’s also a lot smaller—about the size of the trunk of a car, whereas the NIST-F2 takes up an entire room.

Cacs was sent into space on the second Chinese space laboratory, called Tiangong-2, launched from Jiuquan Satellite Launch Centre in Inner Mongolia. Although there are currently no humans aboard, the China National Space Administration plans to send two astronauts to the lab in October to conduct various experiments for a month, as the next step towards launching a full-fledged space station in 2020.