Level 5: A more preferred ideal to shoot for, but does not give extra conformance points than 4. (So that 4 is not considered Level the "best target") Level 4: The desired minimum score. Level 3: Okay (catch-all for near-miss). Level 2: Deficient - But we can't really fail it. Level 1: Poor - Bare minimum even for normal vision. Level 0: Fail
AA is sort of like 1, an inadequate minimum that should not be the goal. AAA is sort of like 3 to 4.
Except both AA/AAA may be too much, or too little, on several cases.