animals, and minerals found in China. For example, Shen noted that the mineral orpiment was used to quickly erase writing errors on paper. Civil engineering The writing of Shen Kuo is the only source for the date when the drydock was first used in China. Shen Kuo wrote that during the Xi-Ning reign (1068–1077), the court official Huang Huaixin devised a plan for repairing 60 m (200 ft) long palatial boats that were a century old; essentially, Huang Huaixin devised the first Chinese drydock for suspending boats out of water. These boats were then placed in a roof-covered dock warehouse to protect them from weathering. Shen also wrote about the effectiveness of the new invention (i.e. by the 10th century engineer Qiao Weiyo) of the pound lock to replace the old flash lock design used in canals. He wrote that it saved the work of five hundred annual labors, annual costs of up to 1,250,000 strings of cash, and increased the size limit of boats accommodated from 21 tons/21000 kg to 113 tons/115000 kg. If it were not for Shen Kuo's analysis and quoting in his Dream Pool Essays of the writings of the architect Yu Hao (fl. 970), the latter's work would have been lost to history. Yu designed a famous wooden pagoda that burned down in 1044 and was replaced in 1049 by a brick pagoda (the 'Iron Pagoda') of similar height, but not of his design. From Shen's quotation—or perhaps Shen's own paraphrasing of Yu Hao's Timberwork Manual (木經; Mujing)—shows that already in the 10th century there was a graded system of building unit proportions, a system which Shen states had become more precise in his time but stating no one could possibly reproduce such a sound work. However, he did not anticipate the more complex and matured system of unit proportions embodied in the extensive written work by scholar-official Li Jie (1065–1110), the Treatise on Architectural Methods (營造法式; Yingzao Fashi) of 1103. Klaas Ruitenbeek states that the version of the Timberwork Manual quoted by Shen is most likely Shen's summarization of Yu's work or a corrupted passage of the original by Yu Hao, as Shen writes: "According to some, the work was written by Yu Hao." Anatomy The Chinese had long taken an interest in examining the human body. For example, in 16 AD, the Xin dynasty usurper Wang Mang called for the dissection of an