According to historical records, Zhang Sui is called thich nhat hanh. Born in Nanle County, Henan Province, he was a famous astronomer and Mr. Feng Shui in the Tang Dynasty. He was born in Xianheng, Tang Gaozong for four years. His great-grandfather was Zhang and his grandfather was Zhang Dasu.

After three years in Chang 'an, his parents died when he just reached the age of weak crown. Later, he decided to become a monk and chose to become a monk. He studied Buddhism and astronomy in Qinshan and studied under master Puji.

During the Kaiyuan period, Zhang Sui accepted the imperial edict of Xuanzong of the Tang Dynasty and came to Chang 'an from the Buddhist temple. He served as a Buddhist adviser to Emperor Xuanzong of the Tang Dynasty in the imperial court. He also participated in the translation of Buddhist scriptures written by fearless master and translated related Buddhist scriptures with other consultants.

In 7265438, the emperor ordered Zhang Sui and his followers to take the lead in revising the new calendar. During the same period, Zhang Sui designed and manufactured astronomical measuring instruments, such as the ecliptic instrument. Using the ecliptic, he successfully measured the coordinates of other stars. There is a big gap between the final measurement results and the measurement data of Han Dynasty. Zhang Sui's measurement data is nearly a thousand years earlier than astronomer Harley's law of self-motion.

In 724 AD, Zhang Sui and other court ministers organized the first large-scale surface data survey in the history of China. His survey covers a wide range, from today's Mongolia to Jiaozhou in Vietnam, including the length of sun shadow and the height of stars in more than a dozen different areas.

The diligent monk also measured the distance between four different areas in Henan Province. The measuring time is set to four solar terms: vernal equinox, autumnal equinox, winter solstice and summer solstice. Record the shadow length of an 8-foot-long pole on the ground under the midday sun, the shadow length of the earth towards the North Pole, and the day and night length of the day. Has the final measurement data changed? The shadow of the sun is an inch away? Conclusion.

The length of the prime meridian can be calculated from the measured data in Zhang Sui, which is a milestone in the history of determining the meridian length by using the observed data.