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» Online Classroom   » Inland and Coastal Navigation   » Public Discussion of Inland and Coastal Navigation   » sextant angle & height

Author Topic: sextant angle & height
Michael Mitgang

 - posted January 25, 2005 11:23 PM      Profile for Michael Mitgang           Edit/Delete Post 
why, when you use the "short cut" H/H(s)/100 you do not use height above line of sight (ie. height of object minus observers height above water)? How should you be treating it if you use a tangent calculation? I would think that in both circumstances you would use height above water, but that does not appear to be how it is shown in the answers. Also, using tangents rather than short cut gives a difference in answer of about 4%. Is that correct?
From: Menlo Park, CA
David Burch

 - posted January 26, 2005 11:05 PM      Profile for David Burch           Edit/Delete Post 
If we worked this out rigorously, our height of eye would be in the equation, and the right formula depends on how far off we are. In the text we give a simple approximation that could easily be 4% or even perhaps a bit more than that in error.

If you want to investigate the correct solution versus tangent or the book approximation, then you can use the NIMA computers that we have presented in our online library.... or you can do it with tables:

see Explanation of Tables

Table 15

Table 16

Table 17

From: Starpath, Seattle, WA

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