http://www.uac.edu.au/documents/atar/2009_table_A3.pdf
Explanation of columns. (All numbers given in the table are out of 50)
First Column -> Course -> Self explanatory I hope.
Second Column -> Number -> Number of students enrolled across NSW.
Third Column -> Type of Mark -> The HSC mark is the mark you see on your final report/sheet thing. This is after it has been aligned and what not. However, the important part in determining your ATAR is the number under the HSC part, the "Scaled" number.
Fourth Column -> Mean -> The average across the state for that particular course.
Eg. In Mathematics Extension 2 the HSC average was 41.7.
While the Scaled average was 44.7.
This means that for that course, on average, students were scaled UP by 3 marks.
Eg. In Aboriginal Studies the HSC average was 37.4
While the Scaled average was 15.4.
This suggests that the course 'Aboriginal Studies' scales VERY poorly.
Subjects that are said to scale "good/well" are those with a scaled mean of 30+
"Average" is around 25 and so on.
Fifth Column -> SD -> Standard deviation -> How much the marks varied from one end to the other end.
Sixth Column -> Max Mark -> Self explanatory. Tells us if the subject is capped or not.
Rest -> P99 P90 P75 P50 P25 -> What percentile those marks lied in.
Eg. If you beat 99% of the state for Maths Extension 2 that places you in the P99 range which means you receive a mark of 48.5 but a scaled mark of 49.4
If you beat 25% of the state you are in the P25 range and you would've received a HSC mark of 39.0 but a scaled mark of 43.3