[pjc50]

It was effectively a "distributed" license key, broken into a large number of parts and structured as a challenge-response, so that it would be difficult to answer without a full photocopy of the manual.

My favourite variant of this was F-19 Stealth Fighter asking you to do aircraft identification, which you could get from the manual .. or any library book on US warplanes.

Least favourite was some game (TMNT?) which printed the codes in gloss black on matte black.

[GuB-42]

Microprose games had awesome manuals. Typically more than a hundred pages full of details going well beyond explaining the game itself. For example, in a flight simulator it had details on every plane in the game, the historical context of the missions, dogfighting techniques, etc...

It wouldn't be out of place in a library.

[rkomorn]

The manual to Grand Prix 2 taught me more about car racing than any other bit of reading, video, or whatever media. It had so much about how to drive, how to use telemetry, etc.

Not that I turned that knowledge into good results but that's another topic.

What a delight that game and its manual were.