When you want to go somewhere, you can easily find your way by using a map app on your smartphone. (10)But do you know how it all happened? (11)A satnav system(卫星导航系统) uses groups of satellites to find out where people are. It sends information to a receiver, like a smartphone. On June 23, 2021, the last satellite of China's Beidou Navigation Satellite System was sent up into space. China's own navigation system was finally completed. It is one of the four navigation systems in the world. (12)
On July 31, Beidou started providing full-scale(全方位的) global services. (13)Since 2000, China has launched(发射) Beidou satellites. Beidou can be used in areas that include farming, public services and business. It has a positioning accuracy(精度) of under 10 metres. People along the Yangtze River used a Beidou-based device to monitor flood waters as well. (14)It allows people to send text messages up to 1,200 Chinese characters in length when mobile phone services are broken by natural disasters.