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HYDROGRAPHIC MANUAL 



Page 246 



Other things being equal, observations on north and south stars are hkely to be 

 more accurate than those on east and west stars, because of the more rapid rate of 

 change in altitude of the latter (see 3384B) . For this reason if more than four stars 

 are observed it is preferable to combine lines of position to a resultant rectangular 

 figure of error whose sides are roughly north-south and east-west. 



Figure 58.— Probable position of ship from stellar observations: A and C— by moving lines of position away from or toward the 

 observed bodies by equal amounts. B and D— by the bisectrLx method. E— by the bisectrix method when there are more 

 than four observations. 



FiGtiEE59.— Position from star sights, using a known figure of error. A. Characteristic figure of error from past experience. B. Char- 

 acteristic figure of error used to determine most probable position from only two star sights. C. Position if lines of position in 

 opposite directions are weighted without taking into consideration characteristic figure of error. D. Position from same lines of 

 position as in C, but taking into consideration the characteristic figure of error. Note that the position is actually nearer the good 

 west line of position than the excellent east one, and that it is almost equidistant from the north and south lines, although one is 

 excellent and one only fair. 



