Ask HN: What's your favorite retro computer manual?

I mean a manual of a hardware or software system published before 2000 that is clear, interesting, insightful, engaging, or otherwise remarkable.

My favorite is the manual of COHERENT, a 1980s Unix System 7 clone for PCs:

http://www.nesssoftware.com/home/mwc/manual.php

The manual provided a comprehensive, clear, coherent (no pun intended) introduction to the system that made me grok Unix and its philosophy.