100 



HANDBOOK OF MAGNETIC COMPASS 



compensation. There are several possibilities of error which may 

 be caught at this time, for example : 



(1) Outside interferences may have been compensated by error. 



(2) In correcting the second vector, the additional electrical 

 load may create sufficient voltage drop in the leads to change the 

 previous adjustment. 



(3) Coil misalignments may create slightly inaccurate compen- 

 sation. 



(4) Poor spacing of compass needles permits sextantal devia- 

 tion errors, due to non-uniform magnetic fields. 



The first three of these errors are easily corrected by repeating the 

 entire sequence of coil compensation — a sort of successive approxima- 

 tion procedure. The fourth error is quite rare and is generally best 

 corrected by replacing the faulty compass. Replacing the coil in- 

 stallation with a type "K" set of coils or a special arrangement of 

 larger coils will also improve the nonuniform field trouble. 



It is also necessary to try each degaussing coil at reversed polarity, 

 individually and collectively, to be sure of reversibility, proportional- 

 ity, and independence of each degaussing circuit and its compensation. 

 Check to see that the coils are not overloaded at this time. Refer to 

 chapter X or XII. 



125. Should it be desired to deflect the compass to relative headings 



\ ^ DEFLECTING 

 laSNST 



FiGCRE 58. — Deflection of compass by magnets. 



