Look
here.But basically all that matters for SAC's is your ranking within your cohort (generally all students taking the subject in your school). This ranking is used in conjunction with the cohorts exam performance to moderate your SAC marks. The moderation process essentially matches the spread of the moderated SC marks with the spread of results on the exam(s), this is achieved by giving first ranking the highest exam mark as their SAC mark, and each of the quartiles the respective exam marks. eg. In a cohort of 100 25th ranking will receive the 25th highest exam mark as their SAC mark and 75th ranking will be given the 75th highest exam mark.
A simplistic, though flawed in some respects, view on moderation is that for your SAC mark you receive the exam score equivalent to your ranking. So if you are ranked 1st you receive the highest exam mark as your SAC mark, if you are 10th you receive the 10th highest exam mark as your SAC mark and so on(if you are ranked nth within your cohort your moderated SAC score will be the nth highest exam score

).
To save confusion I will remind you that
your own exam score does not change under any circumstances,the only exception being if you are granted a derived exam score.