Using Flesh-Kincaid, according to the author of the post, "the most well-known reading comprehension algorithm," hundreds of years of Presidential speeches were analyzed for their grade level equivalency. The result? Go and look. But here some major conclusions from this "analysis":
1. Speeches have grown longer over time.
2. Speeches have grown "less sophisticated" over time.
3. The Gettysburgh Address has an 11th grade reading level.
How useful is this information? It's not. Again, applying readability formulae to, in this case, Presidential speeches, tells us only syllables, sentences, and other measures out of context.