Navigational TrianglesNavigation triangles are normally used as a pair (one against the other) in order to transfer a directional line to a different place on a chart. In this way, they perform similar to parallel rules. Although some triangles are unmarked, others (such as shown here) have protractors imprinted on them. The protractor can aid in drawing a bearing line directly on the chart, and the 90°angle can be useful in constructing lines of position.