## General Concepts

Bridge watch officers have three main duties: Navigation Watch officers process navigation information from several different sources.

Error is the difference between a specific value and the correct or standard value. As used here, it does not include mistakes, but is related to lack of perfection.

In solutions of the sailings, the nofollowing quantities are used: Latitude (L). The latitude of the point of departure is designated $L_1$ ; that of the destination, $L_2$;

The science of Astronomy studies the positions and motions of celestial bodies and seeks to understand and explain their physical properties.

Looking at the sky on a dark night, imagine that celestial bodies are located on the inner surface of a vast, Earth centered sphere (Figure below).