Shen noted the relation of the focal point of a concave mirror and that of the pinhole. Shen wrote extensively about movable type printing invented by Bi Sheng (990–1051), and because of his written works the legacy of Bi Sheng and the modern understanding of the earliest movable type has been handed down to later generations. Following an old tradition in China, Shen created a raised-relief map while inspecting borderlands. His description of an ancient crossbow mechanism he unearthed as an amateur archaeologist proved to be a Jacob's staff, a surveying tool which wasn't known in Europe until described by Levi ben Gerson in 1321. Shen Kuo wrote several other books besides the Dream Pool Essays, yet much of the writing in his other books has not survived. Some of Shen's poetry was preserved in posthumous written works. Although much of his focus was on technical and scientific issues, he had an interest in divination and the supernatural, the latter including his vivid description of unidentified flying objects from eyewitness testimony. He also wrote commentary on ancient Daoist and Confucian texts. Life Birth and youth Shen Kuo was born in Qiantang (modern-day Hangzhou) in the year 1031. His father Shen Zhou (; 978–1052) was a somewhat lower-class gentry figure serving in official posts on the provincial level; his mother was from a family of equal status in Suzhou, with her maiden name being Xu (). Shen Kuo received his initial childhood education from his mother, which was a common practice in China during this period. She was very educated herself, teaching Kuo and his brother Pi () the military doctrines of her own elder brother Xu Dong (; 975–1016). Since Shen was unable to boast of a prominent familial clan history like many of his elite peers born in the north, he was forced to rely on his wit and stern determination to achieve in his studies, subsequently passing the imperial examinations and enter the challenging and sophisticated life of an exam-drafted state bureaucrat. From about 1040 AD, Shen's family moved around Sichuan province and finally to the international seaport at Xiamen, where Shen's father accepted minor provincial posts in each new location. Shen Zhou also served several years in the prestigious capital judiciary, the equivalent of a national supreme court. Shen Kuo took notice of the various towns and rural features of China as his family traveled, while he