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