This is the formula which is used in this tool


gp = 2 + (marks -50) * 1 /15

It means at marks 50 gp is 2
and marks = 80 means gp = 4

e.g. marks = 65 then gp = 2 + (65-50)* 1/15 = 2 + 15 / 15 = 2+1 =3

But if formula is changed then it may be wrong..
If anyone has new formula please post it here, I will try to re program it.

Thanks