MBRA: Reading Difficulty Chart

Box	Boxcar Children (series) (1942 onward). First four books.
BSK	Bailey School Kids (series)
Cat	The Cat in the Hat, by Seuss
D&D	Advanced Dungeons and Dragons manuals (Player's Handbook and Monster Manual)
D2a, D3b, D6b	New Basic Readers (informally, Dick and Jane) (2a, 3b and 6b) (1950s). Look-Say.
E1-E6	Elson-Gray Readers, 1-6 (1930s). Precursor to Dick and Jane. Look-Say rather than phonics
HB	The Hardy Boys (series). 2nd book.
HH	Henry Huggins
HP	Harry Potter and the Sorcerer's Stone
Iliad	The Iliad (Fagles translation)
Land	World Landmark Book #35: Famous Pirates of the New World
M1-M6	McGuffey's Readers, 1-6 (1880s). Phonics.
MTH	The Magic Tree House (series)
LWW	Narnia (series). The Lion, the Witch, and the Wardrobe
ND	Nancy Drew(series)
Pippi	Pippi Longstocking
Roe	Roe v. Wade U.S. Supreme Court Ruling
R&H	Physics by Resnick and Halliday. Freshman college physics text.
ScA	Scientific American biology article
SH	Sherlock Holmes (series)
sm	Spiderman comics
TGB	The Great Brain
Web	Charlotte's Web, by E.B. White
Wonka	Charlie and the Chocolate Factory
WSJ	Year 2006 Wall Street Journal Editorials
[unlabelled dark grey triangle]	"A Picture Book of ..." series by David Adler. Four books.
TtB	Transgressing the Boundaries (explanation)
Oz1, Oz2	First two 'Oz' books by Baum

Things to notice/remember:

This chart does NOT measure all the factors that contribute to reading difficulty. Two obvious missing items are subject matter and total text length.
The McGuffey's Readers do not seem to map to their numerical grade level. What the mapping is, I do not know.
The 1950s Dick and Jane 2nd reader (first book) is easier to read in both vocabulary and grammar than the McGuffey's 1st Reader.
The 1950s Dick and Jane 6th Reader is simpler than the 1930s Elson-Gray 6th Reader. It appears that the 1950s Dick and Jane series is about ½-1 grade level behind the 1930s Elson-Gray series in terms of vocabulary. It is 3-4 years behind in grammatical complexity! Nancy Drew books (considered 4th grade by Lexile) are harder to read than 1950s Dick and Jane 6th grade readers in both vocabulary and grammatical complexity.
Dungeons and Dragons reference manuals are harder in vocabulary than Wall Street Journal editorials, and roughly comparable in grammatical difficulty.
Sherlock Holmes stories are easier in both vocabulary and grammar than an 1880s McGuffey's 5th Reader.
It is difficult to find fiction that has a lexical difficulty greater than 0 (in fact, I have no examples). Lots of non-fiction has a lexical difficulty greater than 0.
Good reading skills are necessary to read scientific texts (e.g. Scientific American articles, college physics textbooks).