The azimuth or bearing of a line along which a ship or aircraft is to travel or does travel for a specified period of time. This definition is also given as the azimuth or bearing of a line along which a ship or aircraft is to travel or does travel, without change of direction, or as the direction of intended motion of a craft in the horizontal plane, measured relative to the water in the instance of a watercraft but relative to the earth in all other craft. It is also given as the direction a navigator wants his craft to travel for a given period of time, or hopes his craft has followed. The direction of a course (d) is always measured in degrees from the astronomic meridian, and that direction is always meant unless it is otherwise qualified as, e.g., a magnetic or compass course.