<What are the FRE units anyway?>

Years and years and decades ago, someone told me about a readability test you could run on a piece of writing to determine how 'difficult' it was. I don't think it was Flesch but cannot for the life of me remember what it was.

I do however remember that the key factors counted were:
- number of passive constructions
- average number of words per sentence
- number of words of three or more syllables (as percent of total words, I think)

These variables were chucked into a calculation and the resulting socre was meant to indicate the number of years of full-time education required to understand the passage in question.

At the time, we had just finished a whole new set of marketing literature for the transportation and distribution (logistics) industry. We ran the test on it and came up with 17 years of education required to understand our pamphlets - this at a time when most of our market were ex-warehousemen or ex-truck drivers. Hmmm...

I also heard apocryphally (a friend of my mother's worked for them) that the UK paper The Sun vetted all articles and allowed no score higher than 6.

later addition to post
Have just remembered that it was the Fog Index - and apparently my memory of factors is somewhat confused too. After a quick google, anyone interested try these links:
http://www.usingenglish.com/glossary/fog-index.html
http://www.usingenglish.com/glossary/flesch-kincaid-index.html