ADJUSTMENT PROCEDURE 57 



of 10.5° E. would be observed and compared with 5.5° W. on 

 180°. Analysis of the deviations on 000° and 180° headings 

 reveals an 8.0° E. C error, which should then be corrected with 

 athwartship C magnets leaving 2.5° E. deviation on both the 000° 

 and 180° headings. All the deviations in column two are now re- 

 calculated on the basis of such an adjustment at 000° heading and 

 entered in column three. Continuing the swing, the deviation on 

 045° would then be noted as 6.4° E. Knowing the deviations on all 

 intercardinal headings, it is now possible to estimate the approxi- 

 mate coefficient D. D is 5.0° E. so the 6.4° E. deviation on 045° is 

 corrected to 1.4° E. and new anticipated values are recorded in a 

 new column. This anticipates a fairly good curve, an estimate of 

 which reveals, in addition to the B of 0.5° E. which was not con- 

 sidered large enough to warrant correction, an A of 1.0° E and an 

 E of 1.5° E. These A and E errors may or may not be corrected, 

 as practical. If they are corrected, the subsequent steps would be 

 as indicated in the last two columns. It will be noted that the 

 ship has made only one swing, all corrections have been made, and 

 some idea of the expected curve is available. 



88. Should the spheres be magnetized, or the permanent B and C 

 magnets be very close to the spheres, any movement of the spheres will 

 change the B and G errors on the compass necessitating readjustment 

 of the B and G corrector magnets. 



Inasmuch as the spheres contribute somewhat to the heeling correc- 

 tion, and the dip needle method of heeling magnet adjustment at dock- 

 side has certain inaccuracies, it would be desirable, if possible, to 

 ref,ne the heeling adjustment under rolling conditions while the ship is 

 on north and south headings. (See chapter XV.) Radical changes 

 in the position of this heeling magnet, with Flinders bar present, may 

 change the deviation curve because of its induction effects on the 

 Flinders bar ; and readjustment of the fore-and-aft B magnets may be 

 necessary. 



Chapter VIII discusses other interaction ejfects between the various 

 correctors. 



89. Deviation curves. — The last step, after either of the above 

 methods of adjustment, is to secure all correctors in position and to 

 sioing for residual deviations. These residual deviations are for 

 undergaussed conditions of the ship, and they should be recorded, along 

 with details of corrector positions, on the standard Navy Form NBS 

 1104 and in the Compass Record Book, NBS 1101. Article 132 dis- 

 cusses the purposes of the various NBS Eecord Forms more fully. 



639720—45- 



