CHAPTER XVIII. SLEWING OF FLINDERS BAR 



141. Tlic need for slewing' Flinders bar is nnicli more rare than that 

 for slevvino; spheres. Also, tlie data necessary for slewing the Flindei's 

 bar cannot he ohtained on a single latitude adjustnfient, as with the 

 spheres. Slewing the bar to some intermediate position is, in effect, 

 merely utilizing one bar to do the work of two ; one forward or aft, and 

 the other port or starboard. 



Article 97 explains that a change of the E./W. deviations with 

 changes in latitude indicates the need for Flinders bar forward or 

 aft of the compass ; and a change of the N./S. deviations with changes 

 in latitude indicates the need for Flinders bar to port or starboard 

 of the compass. 



A change of the B deviations on magnetic E./W. headings is used, 

 as explained in article 97, to determine the proper amount of Flinders 

 bar forward or aft of the compass by calculating the constant c. 



If there is a change of the G deviations on magnetic N./S. head- 

 ings, a similar analysis may be made to determine the proper amount 

 of Flinders bar to port or starboard of the compass by calculating 

 the constant / from : 



f_ T ^i tan Cx-Hj tan CT 

 L ^1 — -^2 J 



when 



X= shielding factor (0.8 to 1.0 average). 



^"1 = earth's field, H, at 1st latitude. 



Ci = degrees C deviation at 1st latitude (magnetic headings). 



Zj — earth's field, Z, at 1st latitude. 



7/2= earth's field, H, at 2d latitude. 



C2=degrees C deviation at 2d latitude (magnetic headings). 



Z2= earth's field, Z, at 2d latitude. 

 Any value of this / constant indicates the need for Flinders bar ad- 

 justment athwartship of the compass, just as a value of the c constant 

 indicates the need for Flinders bar adjustment forward or aft of the 

 compass. The / constant curve in figure 34 (b) is used for the de- 

 termination of this Flinders bar length. If / is negative. Flinders 

 bar is required on the starboard side of the binnacle. 



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