The rubidium atomic clock is the "heart" of the BeiDou-3 satellites. It determines the craft's position accuracy, speed and time functions. Earlier, it usually took about 18 months to deliver a foreign-made rubidium clock to China. Now, it takes the Chinese R&D team around eight months to deliver one. The first China-made rubidium atomic clock was developed between 1996 and 2000. China's first self-developed rubidium clock was successfully tested on a satellite in 2006. Since 2012, China's self-developed rubidium clocks have fully replaced imported rubidium clocks. The clock is designed to lose only a second every 300 million years.