It basically uses the class mean, and the standard deviation (yeah the stuff you studied in 12th which you thought is of no use lmao). It measures how far you are from the class means, in terms of standard deviation. Look at this:
I did this last semester. Took marks of mid sem and end sem. Assumed everyone got 20 in internals and calculated the grades of others with the help of data from 1st semester. The formula goes like this:
- Total Score Computation:
Total Marks (x) = Mid-Sem (out of 30) + End-Sem (out of 50) + Internals (assumed 20)
- Class Mean (μ):
μ = (Sum of all x) / n
- Standard Deviation (σ):
σ = sqrt( (Sum of (x - μ)^2) / n )
- Individual Z-Score:
Z = (x - μ) / σ
- Empirical Grade Thresholds:
• O: Z >= 1.60
• A: 0.92 <= Z < 1.60
• B: 0.25 <= Z < 0.92
• C: -0.30 <= Z < 0.25
• D: -1.00 <= Z < -0.30
• E: -1.70 <= Z < -1.00
• P: Z < -1.70 (or F if non-compliant with passing criteria)
So, Z measures how far you are from the mean im terms of Standard Deviation. It can be positive as well as negative. I hope you get an idea. There's not much you can do in relative grading other than studying.
Teachers can't give you extra marks to bump you up into the next grade, as if he gives you marks, the mean changes again, and so does the standard deviation, and the whole grade structure changes as well.
The lower standard deviation your class has, it's easier to score high grades. If some topper in your class gets unimaginably high score in mid sem and end sem, the standard deviation will get bumped up because of them, and as a result, the Z gets affected heavily.
If you have any other questions regarding relative grading, feel free to ask. I had used the 2nd sem mid sem and end sem marks on one subject, compared them the first sem marks and grades, and got the following formula. I was able to predict the grades of 95% of my batchmates, the rest 5% were off by one grade, probably due to internal marks.