My wife's grandmother was in the WAAF during WWII.

We have her Service Records (1942-44) but are having trouble decyphering some of the terms.
Can anybody help ?

Upon entry to the Service:
Description of Effect = ACH/Ball

Proficiency is graded A, B or C.
I know that A = Skilled at Trade
B = Foreman at Trade
What is C ?

Under 'Special Qualifications', what do the following mean ?
ExRemark (as Balloon Operator)
Exreel (upon promoted to ACW1)
ExReclass (failed an unspecified examination)

Upon discharge from the Service (was pregnant with my wife's mother)
Unit = 652 CL11