How does Guo Shoujing solve the problem of using standard meters?

Since the Tang and Song Dynasties, scientists have made a lot of efforts to solve these problems, but there are no good solutions. Now, these problems are before Guo Shoujing. How to deal with it? Guo Shoujing first analyzed the causes of errors, and then found the corresponding solutions for each reason.

First of all, he tried to increase the length of the face bar of a standard watch to five times, so the shadow was stretched to five times when he observed it. When the shadow is elongated, the error of calculating the time of each solar term in proportion can be reduced accordingly.

He also created an instrument called "Peep a few", so that the watch can also be observed under the irradiation of the stars and the moon.

Secondly, he created an instrument called "shadow symbol", which made the sunlight shining on the gauge pass through a small hole and then reflected to the surface of the gauge, so that the edge of the shadow was clear and the accurate shadow length could be measured.

Guo Shoujing has made a series of improvements to this standard, which has solved many difficult problems in history. His preparation work is better than that of his predecessor.