Transit fix

A transit fix is a position line obtained when two fixed, charted objects come into line, one behind the other, giving a single precise bearing without instrument error. The observer notes the moment the two marks are in transit; the charted line through them is a line of position the ship lies on. Crossing two transits, or a transit with a sounding or a single bearing, fixes the ship. Transits are the most accurate visual line available because they carry no compass error, and charted leading lines and clearing lines used in pilotage are the practical application of the same geometry.