52 HANDBOOK OF MAGNETIC COMPASS 



A is corrected on the standard compass by realignment of the binnacle, 

 and both mechanical A and magnetic A errors are corrected on the 

 steering compass by realignment of the binnacle (see art. 75). On 

 the standard compass, the mechanical A error may be isolated 

 from the magnetic A error by making the following observations 

 simultaneously : 



(1) Record a curve of deviations by using an azimuth (or 

 bearing) circle. Any A error found will be solely magnetic A. 



(2) Eecord a curve of deviations by comparison of the compass 

 lubber's line reading with the ship's magnetic head as determined 

 by pelorus or by gyro. Any A error found will be a combination 

 of mechanical A and magnetic A. 



The mechanical A on the standard compass is then found by subtract- 

 ing the A found in the first instance from the total A found in the 

 second instance ; and is corrected by rotating the binnacle in the proper 

 direction by that amount. It is neither convenient nor necessary to 

 isolate the two types of A on the steering compass and alU A found by 

 using the pelorus or gyro may be removed by rotating the binnacle in 

 the proper direction by that amount. 



The B error results from two different causes, namely : the fore-and- 

 aft permanent magnetic field across the compass, and a resultant un- 

 symmetrical vertical induced effect forward or aft of the compass. 

 The former is corrected by the use of fore-and-aft B magnets, and 

 the latter is corrected by the use of the Flinders bar forward or aft 

 of compass. Inasmuch as the Flinders bar setting has been made 

 at dockside, any B error remaining is corrected by the use of fore- 

 and-aft B magnets. 



The C error has two causes, namely: the athwartsliip permanent 

 magnetic field across the compass, and a resultant unsymmetrical 

 vertical induced effect athwartsliip of the compass. The former is 

 corrected by the use of athwartship C magnets, and the latter would be 

 corrected by the use of Flinders bar to port or starboard of the 

 compass; but, inasmuch as this vertical induced effect is very rare, 

 the G error is corrected by athwartship C magnets only. 



The D error is due only to induction in the symmetrical arrange- 

 ments of horizontal soft iron, a.nd requires correction by spheres, gen- 

 erally athwartship of the compass. 



The existence of E error of appreciable magnitude is rare, since 

 it is caused by induction in the unsymmetrical arrangements of hori- 

 zontal soft iron. When this error is appreciable it may be corrected 

 by slewing the spheres, as described in chapter XVII. 



As has been stated previously, the heeling error is most practically 

 adjusted at dockside with a balanced dip needle. ( See chapter XV) . 



82. A summarv of the above discussion reveals that certain errors 



