As every schoolboy learns, a point has position but no size, and a line has length but no breadth. Nevertheless, to a navigator concerned with fixing his ship, points and lines are represented on his chart as fine pencil marks.

The manner of representing the results of observations as pencil ‘points’ or ‘lines’, has undoubtedly led to the belief that a ship's position must be represented as lying at a point on a position line which is drawn on a chart. Nothing short of perfection in position lines is ever expected by most practical navigators, and two position lines crossing at a point are usually regarded by seamen as yielding a perfect position: and if three position lines meet at a point! … there is seldom even the slightest doubt in the mariner's mind about the reliability of such a fix. On the other hand, three position lines which do not meet at a point are usually regarded as being something not quite respectable.