30 HANDBOOK OF MAGNETIC COMPASS 



Since B is the coefficient of semicircular sine deviation^ its value is 

 maximum, but of opposite polarity, on 090° and 270° headings. The 

 approximate B coefficient is estimated by taking the mean of the devia- 

 tions at 090° and 270° with the sign at 270° reversed. 



2 5= +11.5° +( + 12.5°) = +24.0° 

 ^=+24.0°/2=+ 12.0° = 12.0° E. 



Similarly since G is the coefficient of semicircular cosine deviation, 

 its value is maximum, but of opposite polarity, on 000° and 180° head- 

 ings; and the approximate G coefficient is estimated by taking the 

 mean of the deviations at 000° and 180° with the sign at 180° reversed. 



2 C= +10.5° +( +5.5°) = +16°.0 

 j- I !: ,|6'= + 16.0°/2=8.0°E. 



J^ is the coefficient of quadrantal sine deviation having maximum, 

 but alternately opposite, polarity on the intercardinal headings. 

 Hence, the approximate D coefficient is estimated by taking the mean 

 of the four intercardinal deviations with the signs at 135° and 315° 

 reversed. 



4 Z>=( +20.0°) + ( + 1.2°) + (-8.0°) + ( + 6.8°) = +20.0° 

 Z>=20.0°/4=+5.0° = 5.0° E. 



E is the coefficient of quadrantal cosine deviation having maximum, 

 but alternately opposite, polarity on the cardinal headings. There- 

 fore, the approximate E coefficient is estimated by taking the mean 

 of the four cardinal deviations with the signs at 090° and 270° 

 reversed. 



4 E= ( + 10.5°) + ( -11.5°) + ( -5.5°) + ( + 12.5°) = +6.0° 

 ^=+6.0°/4=+1.5° = 1.5° E. 



These approximate coefficients are estimated from deviations on 

 compass headings rather than on magnetic headings. The arithme- 

 tic solution of such coefficients will automatically assign the proper 

 polarity to each coefficient. 



Summarizing the above we find the approximate coefficients of the 

 given deviation curve to be : 



A= 1.0° E. 



^ = 12.0° E. 



G= 8.0° E. 



D= 5.0° E. 



E= 1.5° E. 



Each of these coefficients represents a component of deviation which 

 can be plotted as shown in figure 21. The polarity of each component 

 in the first quadrant must agree with the polarity of the coefficient. 



