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HANDBOOK OF MAGNETIC COMPASS 



tion in the spheres will there be a change in the deviations on cardinal 

 headings as a result of sphere adjustments. Although sphere correc- 

 tion does not generally correct deviations on cardinal headings, it does 

 improve the stability of the compass on the cardinal headings. 



84. If it were not for the occasional A or ^ errors which exist, the 

 above procedure of adjustment would be quite sufficient; i. e., adjust 

 observed deviations to zero on two adjacent cardinal headings and then 

 on the intermediate intercardinal heading. However, figure 27, show- 

 ing a combination of A and B errors, will illustrate why adjusting 

 procedure must include correcting deviations on more than the three 

 essential headings. 



East ^• 

 2° 



Deg. 

 Dev. 



West 



0° 90° 180° 270° 360^ 



Ccrapass Hd. - Degrees 

 FiGDEE 27. — A and B deviation effects. 



If the assumption were made that no A error existed in the curve illus- 

 trated in figure 27, and the total deviation of 6° E. on the 090° heading 

 were corrected with B magnets, the error on the 270° heading would 

 be 4° E. due to B over-correction. If then, this 4° E. error were 

 taken out on the 270° heading, the error on the 090° heading would 

 then be 4° E. due to B undercorrection. The proper method of elimi- 

 nating this to-and-fro procedure, and also correcting the B error 

 of the ship to the best possible fiat curve, would be to split this 4° E. 

 difference, leaving 2° E. deviation on each opposite heading. This 

 would, in effect, correct the B error, leaving only the A error of 

 2° E. which must be corrected by other means. It is for this reason 

 that (1) splitting is done between the errors noted on opposite head- 

 ings, and (2) good adjustments entail checking on all headings rather 

 than on the fundamental three. 



85. Before anything further is said about adjustment procedures, 

 it is suggested that care be exercised to avoid moving the wrong 

 corrector. Not only will such practice be a waste of time but it 

 will upset all previous adjustments and calculations. Throughout 

 an adjustment, special care should be taken to pair off spare magnets 

 so that the resultant field about them will be negligible. To make 

 doubly sure that the compass is not affected by stray fields from 



