i will do an example of a class with 5 students for a particular subejct
this is how the bos calculate your aligned hsc mark
student -- internal mark (sent in by your school)
bob --------------- 80%
bill ---------------- 75%
ben --------------- 78%
brad -------------- 92%
bango ------------ 45%
total INTERNAL pool of marks = 370 (80 +75 + 78...)
now bos issues percentages of your internal mark over the total internal pool of marks
bob ---- 0.216% (80/370)
bill ----- 0.203% (75/370)
ben ----- 0.211% etc
brad ----- 0.249% etc
bango --- 0.122% etc
ok now internals are finished...thats all we need, lets label those percentages - INTERNAL PERCENTAGES
now the students sit the external exam
bob ----- 75%
bill ------- 81%
ben ------ 62%
brad ------ 89%
bango------73%
now we total the EXTERNAL pool of marks = 380 (75+81...)
now to allocate aligned internal assessment marks, each student gets his INTERNAL PERCENTAGE of the total EXTERNAL pool of marks.
lets call these INTERNAL ALGINED MARKS
bob ---- 0.216% x 380 = 82%
bill ----- 0.203% x 380 = 77%
ben ----- 0.211% x 380 = 80%
brad ----- 0.249% x 380 = 95%
bango --- 0.122% x 380 = 46%
now we take 50% of the INTERNAL ALIGNED and 50% of the EXTERNAL mark
bob ------ 37.5 + 41 = 78.5%
bill ------- 40.5 + 38.5 = 79%
ben ------ 31 + 40 = 71%
brad ----- 44.5 + 47.5 = 92%
bango --- 36.5 + 23 = 59.5%
and abracadbra, your hsc aligned mark for that subject
EDIT: had the cohort done worse in the external exam all up, that is the external pool of marks be less than the internal, then overall each person would get a lower aligned internal mark. If the cohort does better and has a higher external pool of marks than internal, then the internal aligned marks will be higher.
hope u understood all that.
in laymans, the cohort usually does about the same in external pool as internal pool because of statistics and numbers, therefore usually the internal aligned marks end up being roughly the external exam marks distributed in rank order.