D and C category's well explained above. B Cat indicated that the person was above average in his/her role. A Cat was rarely awarded and indicated that the person was exceptional in the role. B and C Cats were the most common on the squadron that I was on in the 70's. Upgrades from the various category's were accomplished with a successful check ride and grilling from the group standardisation unit or GSU. These checks occurred annually. Occasionally interim checks were also carried out.