GLOSSARY 



The following definitions of terms used in this publication are listed for the information of students: 



Air Course. — The corrected compass course steered by aircraft through the air. By combining the Wind Vector and the 

 known Air Speed, the equivalent Ground Course and Speed are obtained. 



Air Speed. — The speed of an aircraft relative to the air. This speed, when known, is represented by a circle of proper 

 radius to the scale in use with its center at w in the Vector Diagram. This circle is treated in the same maimer as ground 

 speed circles drawn with e as their center and used for surface craft. Equivalent Ground Speed is obtained by combining the 

 Air Speed with the Wind Vector. 



Chart Course. — The true direction over the surface of the earth that an aircraft or ship is intended to travel. 



Chart Point. — A properly located point which is fixed in respect to the ground or earth. 



Chart Track. — A line representing the true course and distance made good or desired to be made good between stations on 

 the earth. 



Current Vector. — A vector with origin at e, representing travel of the water over the ground or current. The head of this 

 vector is usually lettered c. It is seldom necessary to use this vector except when anchoring. 



Constant Bearing Line. — The relative line traversed by a unit whose bearing from the reference unit does not change. This 

 condition exists when the guide unit and the maneuvering unit arrive at a common point, diverge from a common point, or 

 when the two have the same vector. In the first case, this is called the "Collision Bearing." 



Guide. — The chosen unit to which movement of other units concerned is referred. In the Relative Plot, the Guide remains 

 stationary. 



Maneuvering Unit. — Any moving unit set up in the problem except the Guide. Specifically, a Maneuvering Unit is one 

 whose movements are under investigation. 



Navigational Plot. — A diagram such as is used in ordinary chart or navigational work. Sometimes the Navigational Plot 

 is used as the alternate solution which may be more rapid than the Relative Movement Plot. Its most common usage is to 

 check or prove the results found in the latter. 



Relative Movement Line. — A line passing through successive relative positions occupied by the Maneuvering Unit plotted 

 from bearings and range-finder distances taken on the Guide, whose position remains stationary in the Relative Plot. It is 

 commonly called a "Relative Line." 



Relative Plot. — One of the fundamental diagrams used in Relative Movement methods. A fixed point indicates the posi- 

 tion of the Guide and one or more Relative Movement Lines are properly related to this point for the movements of the Maneu- 

 vering Unit. This diagram yields position, as well as direction and distance of relative travel. 



Relative Position. — The position occupied by one unit with respect to another, defined by range and bearing of one from 

 the other. The bearing may be either true or relative. 



Slope. — A direction or inclination. This term is usually used in connection with the transfer of a fine parallel to itself 

 from one diagram to another. 



Speed Circle. — A circle drawn about a point or the end of a vector with the radius equal to a given speed. Such circles 

 drawn with e as center indicate speed over the ground. If drawn with w as center they indicate speed of aircraft through the air. 



Time Line. — A line joining the heads of two vectors which represent successive courses and speeds of a specific unit in 

 passing from an initial to a final position in known time, via a specified intermediate point. This line also touches the head of a 

 constructive unit which proceeds directly from the initial to the filial position in the same time. By general usage this con- 

 structive unit is called the Fictitious Ship, and the head of its vector, marked "/," divides the Time Line into segments inversely 

 proportional to the times spent by the Reference Unit on the first and second legs. The Time Line is used in 

 two-course problems. 



Vector.- — A straight line which indicates by its inclination and length respectively the direction and rate of travel of a unit 

 represented by the head of the vector relative to a unit represented by the foot of the vector. 



Vector Diagram. — A coordinated set of vectors representing concurrent travel of the units concerned. It is a fundamental 

 diagram in the Relative Movement Method. This diagram yields rate and direction of travel. 



VII 



