Found this post at Jiblog, which led me to this: a readability test for websites.

Before I go any further, Microsoft Word used to do something similar for documents. Can't seem to find it now. Did they remove it?

Anyway, here's what the results mean:

The Gunning Fox Index: the number is supposed to correspond to a rough grade level. Here's what they say the numbers mean:
6: TV guides, The Bible, Mark Twain
8: Reader's Digest
8-10: Most popular novels
10: Time, Newsweek
11: Wall Street Journal
14: The Times, The Guardian
15-20: Academic papers
Over 20: Only government sites can get away with this, because you can't ignore them.
Over 30: The government is covering something up.

The Flesch Reading Ease Index is an index number that rates the text on a 100-point scale. The higher the score, the easier it is to understand the document. Authors are encouraged to aim for a score of approximately 60 to 70.

And the Flesch-Kinkaid Grade Index is another rough measure of how many years of schooling it would take someone to understand the content.

Now, to the results:

Grandpa John's:
Gunning Fog Index 8.35
Flesch Reading Ease 71.89
Flesch-Kincaid Grade 5.67

Mr. Pterry:
Gunning Fog Index 8.51
Flesch Reading Ease 73.57
Flesch-Kincaid Grade 5.32

Old Whig:
Gunning Fog Index 9.25
Flesch Reading Ease 66.94
Flesch-Kincaid Grade 5.93

And, no surprise, the least-readable award goes to...

Steve's Jawbone of an Ass:
Gunning Fog Index 9.40
Flesch Reading Ease 72.77
Flesch-Kincaid Grade 6.24

The test measures other things, too: counts numbers of words of 1, 2, 3, and 4 or more syllables, things like that. Check it out.