PB in my stats board is like this stated in the FAQs of the intranet (HR) is 1.5mths to 4 mths

Actual fact is

Default is C for most people

C = 1.5 mth
C+ = 1.75 mth

B = 2 mth
B+ = 2.5mth

A = 3 mths
A+ (V.Outstanding) = 4 mths

B+ to A+ are reserved for Scholars
B is reserved for non-scholar who know how to suck up on their bosses

C+ for those who know how to wayang

C for those who are honest and hardworking down to earth but non of the above