Scaling in Methods weird

[Jemin99]

So for methods
2012, according to grade distribution
A+ for exam 1 was 73~80
For exam 2 was 123~160, 45 scaled up to 47.8

2013,
A+ for exam 1 was 72~80
For exam 2 was 123~160, 45 scaled up to 49.7

So exams difficulty was about the same but scaling was much different to each other
How does scaling work?. Wahh?

[Buddster]

Scaling is based on how well people do in other subjects. For example, if everyone who does methods does really well in all their other subjects it scales up. Mathematics subjects are scaled against each other as well, using this method.

http://www.vtac.edu.au/results-offers/atar-explained/scaling.html