HEADING 41 



chart. Multiple ranges consist of several markers in the background 

 and a single marker in the foreground, or vice versa. The ship is 

 brought to the desired compass course and, at the instant of crossing 

 the line of sight of the range, a bearing is taken with the azimuth 

 circle or pelorus. With the azimuth circle, the difference in degrees 

 between the observed bearing of the range on the face of the compass 

 and the known magnetic bearing of the range is the deviation on 

 that compass course. If using a pelorus, the forward sight vanes 

 are set to the magnetic bearing of the range and the magnetic heading 

 of the ship is read under the forward lubber's line of the pelorus at 

 the instant of taking a sight on the range. The deviation is the dif- 

 ference in degrees between the compass heading of the ship and the 

 known magnetic heading of the ship as indicated by pelorus. 



56. Deviations on compass courses may be obtained by the use of 

 reciprocal hearings. A pelorus is set up on shore and the south end 

 of the dial is aligned with magnetic north. A ship can then sight 

 the pelorus on shore, using an azimuth circle or pelorus, at the same 

 instant the observer on shore sights the ship. The ship's bearing 

 from shore on the reversed pelorus is the magnetic bearing of the shore 

 position from the ship. Continuous communication between ship 

 and shore is necessary and must be so arranged as to provide simul- 

 taneous observations. Two methods of such communication are by 

 flashing lights and, preferably, by short range two-way voice radio. 



Additional methods of determining deviations are by the use of 

 azimuths of the moon, stars, and planets. For detailed information 

 as to the calculation of the azimuths of these celestial bodies, consult 

 any standard work on celestial navigation. 



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