HEADING 37 



(2) In correcting (going from compass to magnetic to true), 

 apply the sign algebraically ( + East,— West). 



In uncorrecting (going from true to magnetic to compass), 

 reverse the sign ( — East, + West). 



Complete facility v)ith such conversion of heading data is essential 

 for expeditioms compass adjustment procedure. 



Typical heading relationships are tabulated below : 



Compass heading 358°, magnetic heading 003°, deviation 5° E. 

 Compass heading 181°, magnetic heading 179°, deviation 2° W. 

 Compass heading 040°, deviation 3° E., magnetic heading 043°. 

 Compass heading 273°, deviation 2° W., magnetic heading 271°. 

 Magnetic heading 010°, deviation 2° E., compass course 008°. 

 Magnetic heading 270°, deviation 4° W., compass course 274°. 

 Magnetic heading 358°, variation 6° E., true heading 004°. 

 Magnetic heading 270°, variation 6° W., true heading 264°. 

 True heading 000°, variation 5° E., magnetic heading 355°. 

 True heading 083°, variation 7° W., magnetic heading 090°. 



47. Use of compass heading and magnetic heading for adjust- 

 ment. — The primary object of adjusting compasses is to reduce devia- 

 tions (to make the niagnetic heading and the compass heading iden- 

 tical, or as nearly so as possible). The two methods of accomplishing 

 this are as follows: 



(1) Place the ship on the desired magnetic heading and cor- 

 rect the compass so that it reads the same as this magnetic head- 

 ing. This is the preferred method. 



(2) Place the ship on the desired conhpass heading and deter- 

 mine the corresponding magnetic heading of the ship, and correct 

 the compass so that it reads the same as this known magnetic 

 heading. This method is used whenever it is impractical to place 

 the ship on a steady magnetic heading for direct correction. 



In using the magnetic heading method.^ the deviations of the com- 

 pass are easily observed as the difference between the compass reading 

 and the known magnetic heading of the ship. The difficulty in using 

 this method lies in placing the ship on the desired magnetic heading 

 and holding the ship steady on that heading while adjustments are 

 being made. 



When using the compass heading method^ the ship can easily be 

 brought to any desired compass heading, but the difficulty is in the 

 determination of deviations. Further difficulty arises from the fact 

 that the steersman is steering by an uncorrected compass whose devia- 

 tions are changing as the necessary adjustments are being made. 



