To my understanding, it works like this.
50 marks from school assesments
50 marks from the writen HSC
= 100 total marks, which then are scaled, and the top 10 units are added
Your number goes into some huge list,
Some computer spits you a number.
So this means that if you get an assignment, and its weighed lets say 20%, that means really, 10%.
Hope i make sense
EDIT: The 100 marks is for every subject.