a) How does marks in A Levels calculated to enter Uni ?

A-level grades are calculated on a lettered grading scale (A, B, C, D, E, S, U). S means a sub-pass or pass at O-levels. U means failure (even at O-levels). S and U are failing grades at A-levels. Universities convert those grades on a scale into ranking points. Therefore, your 3 H2 (full A-level subjects), 1 H1 (AO-level subject or worst H2 subject if you are taking 4 H2 subjects) and H1 General Paper are taken into account. 

For the H2 subjects: 
A = 20 
B = 17.5 
C = 15 
etc…

For the H1 subject (or your worst H2 subject) and General Paper 
A = 10 
B = 8.75 
C = 7.5 
etc…

When you sum up all the points, you get the university ranking points which is considered for admissions to local universities.

b) How come if student take 4 subjects, I read that student getting 9 distinction ?

You take more than 4 subjects in A-levels. You just take 4 academic subjects. For instance, you could take the following combination to get 9 distinctions while staying within 12 academic units:

H2 Mathematics – A 
H2 Physics – A 
H2 Chemistry – A 
H1 Economics – A 
H3 Physics – Distinction 
H3 Chemistry – Distinction 
H1 General Paper – A 
H1 Project Work – A 
H1 Chinese (Mother Tongue) – A

*Each subject at A-levels is assigned a point value. MOE allows you to take up to 12 points (or on special appeal – 13 points). All H2 subjects are assigned 2 points and all H1 and H3 subjects are assigned 1 point each.

You have to take H1 General Paper (unless you take H2 Knowledge & Inquiry), H1 Project Work and H1 Mother Tongue (you are exempted from actually taking the H1 MT paper if you passed HCL in secondary school but it still counts as one point). That leaves you with 9 points to play with. Most people at top schools will choose 4 H2 subjects and 1 H3 subject.

H1 PW = 1 point 
H1 MT = 1 point 
H1 GP = 1 point 
H2 Physics = 2 points 
H2 Chemistry = 2 points 
H2 Mathematics = 2 points 
H2 Economics = 2 points 
H3 Essentials of Modern Physics = 1 point

Total: 12 points (or academic units as MOE calls them).

You must also take subjects from both arts and science. For instance, you cannot take Physics, Chemistry, Mathematics, Biology – which are all science subjects.

c) How come the results of some are shown as 9 Distinctions ? I thought it is supposed to be grades like A, B, C or D ? No ?

An "A" is considered a Distinction.

d) What does Perfect scores means ?

It means you have scored A for every single paper you took.

e) What does H2 passes or H2 Distinctions means ?

H2 distinctions just means scoring A in the H2 subject.

f) What does Principal paper & subsidiary paper means ?

No idea. I don’t think we use that term any more.

g) What is Special Paper ? 

It used to mean Paper 0 – a more difficult subject paper of the same subject. It has been superseded by "H3"-level subjects.

A lot of H3 Subjects are on offer, but you have to get good grades and meet school criteria to be able to take it. Most H3 subjects start at the beginning of J2. It is like HMT in PSLE in a sense that it is optional and more advanced than your normal subjects. You would also have to take the corresponding H2 subject to take a H3 (for instance – you cannot take H3 Essentials of Modern Physics without taking H2 Physics, that would be like taking Higher Chinese without taking Chinese).

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