Dead reckoning (DR)

Dead reckoning advances a known position by applying the courses steered and the distances run through the water, without reference to any external fix. It uses heading and log speed only, so it ignores the set and drift of current and the leeway from wind, which is why a DR position must be converted to an estimated position once those are allowed for. DR remains the backbone of position-keeping between fixes and the fallback when GNSS and visual references fail, and every chart-work and ECDIS system maintains a continuous DR track.