Where the primary meridian passes. The ticket is a paper numbered bracelet. Standing on the ground with two legs and taking pictures on the first meridian is a must for every visitor. The meridian sign is copper. It is also engraved with measuring instruments and time-reporting devices in the houses at the end of every major city in the world, including Beijing. It's kind of like a science pavilion. So many primary and middle school students are guided by their teachers.