Twurp's Peerage

The Discworld’s Burke’s Peerage, and the entry is here because of what Vimes does with it rather than what it contains.

Reference books encode whose account of the past is official. A peerage exists to make descent look orderly and inevitable — to convert a few centuries of successful violence into a tidy tree of names with dates attached. Vimes, who is descended from the man who executed a king and has been reminded of it his whole life, reads it the way a copper reads any document produced by interested parties: with attention to what has been left out.

That makes it a close relation of Bathilda Bagshot’s A History of Magic, filed a universe away. Both are the standard, respectable, approved account. Both are accurate about everything except the part that matters. The difference is that Rowling’s textbook is exposed by a journalist, and Pratchett’s is exposed by a policeman who was in it all along.

On the readability rating. Consulted repeatedly and characterised precisely; never quoted at length. We know its editorial posture far better than its prose.