COMPASS RECORDS 113 



ary battle compasses shall be prepared and kept posted near those 

 compasses in such positions as to be accessible to the officer of 

 the deck and other officers concerned in the navigation of the 

 ship. Deviation -tables, on form NBS 1104, for all compasses in- 

 stalled, shall be entered in the Compass Kecord at the end of 

 every quarter. 



"8. Annually, on June 30, all vessels shall submit to the Bureau 

 of Ships Forms NBS 1102 and 1104 completely filled out. 



"9. An error in the variation affects the constant coefficient 

 A by an amount equal to the error. Once accurately determined 

 (preferably by the method of reciprocal bearings) the A should 

 be used as a constant correction to the variation as obtained from 

 the mean of the errors observed on the equidistant compass 

 headings. 



"lb. Vessels equipped with degaussing coils should be supplied 

 with electromagnetic compass compensating coils. These coils 

 after proper adjustment should not require frequent resetting. 

 Their operation should frequently be checked, however, to make 

 sure that no failure has occurred. It is advisable to observe and 

 record the deviations whenever a routine test of the degaussing 

 coils is made, as well as when a complete swing for deviations is 

 made. Vessels equipped with degaussing coils but no compass 

 compensating coils should swing ship with coils energized at 

 each appreciable change in magnetic latitude." 



Bureau of Ships, August 19Jj.l. S. M. Robinson, 



Chief of Bureau. 



All the NBS forms listed above must be kept accurately and up to 

 date in the Compass Record Book, and submitted to the Bureau of 

 Ships as required, since these records provide the complete history and 

 are the basis of all calculations concerning the Compasses on board 

 ship. 



NBS Form 1103, Napier's Diagram for Plotting the Curve of 

 Deviations, is discussed and illustrated in article 42. NBS Form 1104 

 (revised November 1943) is discussed and illustrated in articles 89 and 

 90. NBS Form 1106, Analysis of Deviations, is used in its entirety 

 for analysis of exact coefficients when {a) the vessel is newly com- 

 missioned, (b) the vessel is on or near the magnetic equator, and (c) 

 the vessel undergoes major structural alterations or repairs. This 

 analysis form is generally used for data taken with all correctors 



