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.
What was the book Wubei Zhi (A Treatise on Armament Technology) about?
The book Wubei Zhi (A Treatise on Armament Technology) included Zheng He's sailing charts, the Mao Kun map, tracing back to Zheng He's and earlier voyages.
Who published the book Wubei Zhi in 1628?
The Wubei Zhi was compiled in 1621 by Mao Yuanyi (茅元儀 Máo Yuányí; 1594–1640?), an officer of waterborne troops in the Ming Dynasty.

Question: What was the book used for ?
Self-contained rewrite: What was the Wubei Zhi used for?