What are the uses of ancient watches?

The ancient standard table has a wide range of uses: the number of days in a tropical year can be determined by the periodic change of shadow length; 24 solar terms can be inferred by measuring the shadow length of the sun at noon; When the shadow is due north, it is noon when the sun is seen; Used to correct pot leakage and so on. The length of the ancient representative was set at 8 feet, which took a long time. In the Yuan Dynasty, Guo Shoujing's improved "high table" was four times higher than the ancient "eight-foot table", and some accessories were added, which overcame the shortcoming that the end of the sun shadow was blurred in the past and improved the accuracy.