The so-called "space-time satellite" refers to the number of space-time satellites that stay in the same space-time grid as the confirmed number for more than 10 minute within 800 meters, and the cumulative stay time of any number in the recent 14 days exceeds 30 hours. Because the system test shows that they have been in the same space, they will have more opportunities to contact cases than others, but they may not know that they have been in the same place, so the health code will turn yellow to remind the public. In addition, if you have lived in a high school risk area in the last 14 days, or stopped for a while, the green code will also turn into a yellow code. But it has not been in the middle risk area, just because the network coverage is not very accurate, so it has been displayed. If it passes near a medium-risk area, the health code may turn yellow. So what should I do after the health code changes from green code to yellow code? The staff said that it is necessary to conduct nucleic acid sampling and testing, and the test results will be directly related to the health code. If the result is negative, the health code will automatically become a green code.