It requires that the navigator know three things, as shown in the illustration below: (1) his ship’s starting point, (2) its speed, and (3) its heading (direction of travel).
Lai to noteiktu, seno laiku jūrniekiem bija jāzina (skatīt attēlu apakšā) 1) kuģa maršruta sākumpunkts, 2) tā ātrums un 3) kurss.