How to use the Readability Graph.

Randomly select three 100-word passages from a book or an article.
Plot the average number of syllables and the average number of sentences per 100 words on the graph to determine the grade level of the material.
Choose more passages per book if great variability is observed and conclude that the book has uneven readability.
Few books will fall into the solid black area, but when they do, grade level scores are invalid.

Additional Directions for Working Readability Graph

Randomly select three sample passages and count exactly 100 words beginning with the beginning of a sentence. Don't count numbers. Do count proper nouns.
Count the number of sentences in the hundred words, estimating length of the fraction of the last sentence to the nearest 1/10th.
Count the total number of syllables in the 100-word passage. If you don't have a hand counter available, an easy way is to simply put a mark above every syllable over one in each word, then, when you get to the end of the passage, count the number of marks and add 100.
Enter graph with average sentence length and number of syllables; plot dot where the two lines intersect. Area where dot is plotted will give you the approximate grade level.
If a great deal of variability is found, putting more sample counts into the average is desirable.