From emails I receive from UNSW they don't use WAM. It's solely based on 25% UAI and 75% GPA.
To work out your GPA. Grade = HD = 7, D = 6, C = 5, P = 4, F = 0.
Grade x Credit Points
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Sum of Credit Points
Eg. Semester 1 you did 4 subjects each worth 6 credit points...