CHAPTER XVII. SLEWING OF SPHERES 



139. Figure 19, The Suiimiiiry of Compass Erroi\s and Adjustments, 

 outlines the use of spheres for correcting all quadrantal errors. It 

 will be observed that spheres are used athwarlship to correct plus 

 D (easterly) error and fore-and-aft to correct minus D (westerly) 

 error. Should the quadrantal deviations be of an E^ rather than a 

 D nature, correction is achieved by placing the spheres on either of 

 the intercardinal axes, as shown. Generally, the E error is so small 

 that correction is unnecessary except on compasses which are mounted 

 unsymmetrically with respect to the masses of metal in the ship. 

 However, when E error does exist, it is usually in conjunction wdth 



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J vv 





'RcsuHani 



C^ucidfanfaf 

 fCarvz 



CuJSVB'S 



Figure 61. — Vector analysis of quadrantal error. 



D error, and the typical problem involving E error requires a correc- 

 tion for both the D and E components. Such correction could be 

 achieved by using two sets of spheres on the appropriate axes, but 

 it is more logically made by placing the existing set of spheres on 

 some intermediate axis so as to correct the resultant quadrantal error 

 directly. 



Inasmuch as the D and E coefficients represent two quadrantal sine 

 functions whose phase positions are 90° apart, their resultant effect 

 will also be a quadrantal sine function of larger magTiitude, at some 

 intermediate phase position. Since this problem involves the addi- 

 tion of two sine functions, a vector analysis is convenient for deter- 

 mining the magnitude and phase position of the resultant quadrantal 

 error. 



121 



639720—45- 



