bassicaly look here for more about the frequency
http://ooakforum.com/viewtopic.php?f=43&t=31831
according them it is defined something like this
Under 1,000 is DEF
1000 - 1,100 ALL
1,100 - 1,250 ALL+
1,250 - 1,400 OFF-
1,400 - 1,600 OFF
1,600-. OFF+