I have two items for you.
First, an excerpt from the 2002 Scaling Report -
The model underpinning the scaling algorithm specifies that the scaled mean in a course is
equal to the average academic achievement of the course candidature, where for individual
students, academic achievement is defined as the average scaled mark in all courses
completed. This leads to a set of simultaneous equations from which the scaled means of 2
unit courses were obtained.
The scaled standard deviation for a course was set equal to the standard deviation of the
academic achievement of the course candidature.
Second, an example document in simple-to-understand language - <a href=/other/Scaling_UAI.pdf target=_blank>here.</a>
Note that, whilst some parts of the document are no longer relevant (e.g., the scaling process is now performed by the Technical Committee on Scaling, not the University of Sydney) it can still assist you in understanding, at least conceptually, how it is done.