My wife just told me about the SMOG readability formula, which is evidently widely used. “SMOG” stands for Simple Measure of Gobbledygook. It looks for the number of polysyllabic words (3 syllables or more) used in a document. The square root of the result of dividing the number of polysyllabic words by the number of sentences is used to derive a readability grade level; read more on Wikipedia.
I ran the calculator here on a few passages in our book (those without equations, which I thought would throw the calculator off): Deferred Shading, Fresnel Equation, Scene Graphs, and the final chapter. Scene Graphs was simplest, at 12.56, Fresnel hardest, at 14.1. On average the level was a bit above 13, meaning College Freshman level. Pieces such as this one weigh in at 17.12. I took a piece of text from Hearn and Baker’s old Computer Graphics, C Version, 2nd Edition, on Fractals, and it came up as 14.47. So our book’s no Hop on Pop, but it’s at least not horrifically hard and seems in the ball park for our target audience.
By the way, this post’s SMOG grade is 11.21.