Originally Posted by Tinkermaster

There is a quota to every subgrade.
Usually up to 35% for As or Bs.
Up to 55% for As+Bs+C+
The rest will be Cs.
If the number of teachers of a job grade exceed a certain quota, then there will be a C-. appearing. Performance is now rated on a relative scale.

So it is not the panel of KPs in the ranking panel who determined the percentage.They can just collectively come up with a decision whether an officer meets the KRA for the job grade and put them in a ranked order. And there must be differentiation when a C grader is compared to a C+, or a C+ with the B grader. So if anyone gets a C-, it means there are some areas the person is not doing well in. Usually one can also tell, if one is already not getting a A/B/C+ when you are in your lower sub grades, the chance of you excelling when you are at a higher sub grade is usually slim.