An ongoing ATAR mystery for many people is why the maximum rank is 99.95, instead of the 100 awarded to the best in the state under the previous Universities Admission Index (UAI) system.
The first reason is that it brings NSW in line with other states and territories, which were all providing a maximum rank of 99.95 under different names by the time the ATAR was introduced in NSW in 2009.
"It made the ATAR more portable," said Donna Munro, community liaison manager at the Universities Admissions Centre (UAC).
The second reason is that "a rank of 100 is statistically anomalous", according to Ms Munro.
"In other words, it's not entirely possible because a rank of 100 means you have beaten 100 per cent of your cohort, including yourself.
"The highest is 99.95 because ATARs are in increments of 0.05. If we had an ATAR at every decimal place, we could have had a maximum rank of 99.99."
 
Increments of 0.05 were put in place mainly to make rankings more manageable for universities.
"We end up with around 40 or 50 people at each increment, so universities know that there are around that many at each one."
A total of 47 students achieved an ATAR of 99.95 this year.
The ATAR is calculated from a student's best 10 HSC units, including at least two units of English.
 
Raw HSC marks are scaled to make different courses comparable "in the same way that an exchange rate can be used to compare currencies", according to UAC.
The scaled mark is then used to rank students. Universities make admission offers based on the number of places available for a course, the number of students who have applied and their ATARs.
The ATAR system is now used by all states and territories except for Queensland, which provides an Overall Position (OP) to year 12 leavers, and is an internationally recognised qualification.
