I’m not sure if I have a previous post on this or not. It seems to have disappeared. Fog does seem to hide things, doesn’t it?
The Gunning Fog Index measures what grade level a section of writing is. It takes into account word length, sentence length, and syllable count. I do not think it is the most reliable way to judge grade level. Taking into consideration the rate at which schools teach larger words now, it does not fit.
On the other hand, I can see how it would be useful. Documents that are for law purposes often seem to come out in a language that the average person would definitely not understand. Using the fog index would definitely help the creators of those documents to make their paperwork much easier and clear cut.