Permaculture: A Designers' Manual - Title

Quoting Geoff Lawton from Podcast #280 on paying attention to every word in the Permaculture Design Manual:

"I think about every single word in that manual like your listeners are doing...I even analyze it with my students: why he {Mollison} called it a manual." He goes on to describe it "like a car manual."

So why did Bill call it a manual?

Manual

noun
1.
a book of instructions, esp. for operating a machine or learning a subject; a handbook.

synonyms: handbook, instructions, guide, how-to book, primer, guidebook

I believe its just the proper term for the book of papers he assembled.