Conversation so far:
What were Zheng He's sailing charts ?
Zheng He's Mao Kun map was 40 pages which vary in scale from 7 miles/inch in the Nanjing area to 215 miles/inch in parts of the African coast.

Question: What was the book about ?
Self-contained rewrite: What was the book Wubei Zhi (A Treatise on Armament Technology) about?