For advance and challenging courses undertaken in one's undergraduate academic career, absolute grades or GPA does not necessarily indicates the abilities of a student. This is especially so where grade inflation is more rampant than before and tougher courses are not weighted. Class rank might be a more accurate way to signal that student's abilities relative to his/her cohort. In particular, the physics department with which I did my undergraduate do not partake in scaling of grades.
Suppose I would like to obtain my class rank after graduation, what would be the most appropriate channel to do so?