For a number of years past the writer has employed in chart work certain uniform symbols which have proved so convenient that he feels justified in recommending them to others. In the absence of such a system of symbols it is usually found necessary to indicate in writing, abreast each position plotted on the chart, the method by which the position was determined; this takes time, needlessly disfigures the chart, and frequently covers space required for other purposes.
The symbols which, after considerable trial, seem to cover all needs are only three in number and are shown in the accompanying illustration.
The first, (a), consisting of a dot surrounded by a circle, is used to indicate positions “ by observation.” These include fixes from bearings of terrestrial objects as well as from the intersection of lines of position derived from celestial bodies—in short, all accurately determined positions are thus indicated.
The second symbol, (b), consisting of a cross with arms intersecting at the point of reference, is used to indicate positions “ by dead reckoning.”