GRaphite rod blanks

Question
I am a very avid angler as is my father, and I am also well studied in chemistry but I have a question that I cannot find an acceptable answer for, what does the IM number on a graphite rod blank mean? (ie. IM6, IM7, etc.) and why is a higer number better? does the designation have anything to do with the manufacturing standards, or just simply the way the graphite polymer is put together?

Thanks
Kevin Edwards

PS, feel free to post this on your message board, I don't think I am the only one that would like some clarificatrion on the issue

Answer
intermediate modulus (fibers ) it relates to graphite  and fiberglass rods
Read about what little  I know at
http://community-2.webtv.net/fishing-folks/Graphiteaprimeron/

or in The Technology of Fly Rods  by Don Phillips .
As for me I like powerfibers in bamboo better than dead chemicals.