Measuring Bearings on the Chart

A parallel ruler, rolling ruler or navigational plotter transfers the direction of a charted line to a compass rose or meridian. The instrument should remain aligned with the intended line while it is moved; a small slip can create a significant cross-track error over a long leg.

Read the true graduation indicated by the chart or plotter and state the answer with three figures and a T suffix. Do not assume one ring is always correct from its position alone: inspect the labels and arrow direction on the instrument or rose.

A line has two directions separated by 180°. Before recording the answer, ask which way the vessel, bearing or route leg is intended to point. A line from A to B may be 068°T while the same line from B to A is 248°T.

For a corrected true bearing observed from the vessel to a charted object, plot the reciprocal from the known object. One bearing creates only a line of position; it does not create a complete fix until combined with sufficient independent position evidence.