American system GPA = Grade Points Average

NUS CAP = Cumulative Average Point

GPA (out of 4)= CAP (out of 5)

SAP in NUS, if I remember correctly, is semestral average point

SAP is the average of semester result in question.

e.g.
Sem 1 (M1, M2)
M1 4MC 5
M2 4MC 5

SAP (Sem 1)=5
CAP=5

Sem 2 (M3, M4, M5)
M3 4MC 4
M4 4MC 4
M5 4MC 4

SAP (Sem 2)=4
CAP=4.5