Definition
When two charted objects appear one directly behind the other, the observer lies on the straight line joining them. That line is drawn on the chart and is far more accurate than a compass bearing because no instrument error is involved. Transits are used to check compass deviation, to mark the edge of a hazard, and as leading lines into harbour. Accuracy improves as the ratio of the distance between the two marks to the observer's distance from the nearer mark increases.
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