1) Consistently accurate 2) Dead accurate 3) Inerrable 4) Inerrant 5) Infallible 6) Not erring 7) Not liable to error 8) Perfect 9) Precise 10) Right on the mark 11) Straight to the mark 1) Inerrable 2) Inerrant 3) Infallible 
• (a.) Committing no mistake; incapable or error or failure certain; sure; unfailing; as, the unerring wisdom of God.
unerring, unerringly 1. Unfailingly accurate or correct. 2. Committing no mistakes; consistently accurate.
not erring; not going astray or missing the mark: The captain set an unerring course for home. · undeviatingly accurate throughout; not containing any error or flaw: She gave an unerring recital of the day's events. · invariably precise or correct: unerring taste.