like all other language subjects, i THINK you have to get either 80s or 90s to be scaled up and if you get lower it scales you down... not sure but my teacher told me this ...
not sure about this but i heard that arabic scales like shithouse
thers a document lying around and if i get around to it, ill post it up http://www.boredofstudies.org/scaledmeans.php
have a look at the document...it is the scaling of courses freom 2001-2003
itll give you a fair idea on its scaling