Basically, you already know that scores for subjects are given out of 20. With these Adelaide Headstart subjects, the scaling on them is pretty much broken in a good way for you. For example, to get a 20/20 in a SACE Biology, you'd need to get A+ overall grades for assignments, tests and the exam, quite a difficult feat. However with Headstart Human Bio, you'd just need to end up on HD overall for the subject, this may sound difficult but you'd only need to end up on at least an 85% to get a HD whereas in SACE biology you need to average 96%+ for tests, A+ assignments and an A+ on the exam which is quite difficult. Even if you don't get 85%, even a 75% overall of D will give you a 19.8/20. Maintain that score in a SACE subject usually gives around 15-6.