Μῶμος found fault in the gods' perfect works: the bull whose horns sat below its eyes, the house that could not roll away from bad neighbours, the goddess whose sandals squeaked. Some faults are real and fixable; some are carping — a fault found because faulting is the job. The critic's own worth is whether he can tell them apart.
Each 'work' carries some true faults (fixable defects) and some flawless features. A fair critic flags a feature only when it is genuinely faulty; a carping critic finds fault everywhere, catching real faults but also inventing false ones. The instrument tallies, across works, the real faults caught, the carps (false faults raised), and the real faults missed — so the critic is scored on precision and recall, not on how much fault they find. Momus's gift is only worth its accuracy.
'Fault' is a clean binary per feature here; real critique is graded and contestable, and one person's carp is another's standard. The measured thing — that finding more fault is not the same as being right, and a good critic is scored on hits vs false alarms — is the honest core, and the whole ethic of this domain.
A critic who flags everything is never wrong about the faults that exist — and never trustworthy, because he is also never wrong about faults that don't. Perfect recall bought with zero precision is not criticism; it is noise wearing criticism's clothes. This is Momus's own trap.