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Author
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Topic: RFix....when to adjust DR
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Jon
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posted January 05, 2021 09:32 PM
Since being introduced to running fixes in the home study CN book, I've felt as if I didn't 100% "get it." This really came to the fore while working through HBS without checking my answers thoughout the problem sets.
Issue #1: Rather than simply marking down the first LOP and continuing with my course plotting, I arbitrarily adjusted my DR--what I called DR'--to someplace on that first LOP. I know realize that it's much simpler and cleaner to make my adjust after RFix (post-LOP #2).
Issue #2: Is there any reason to try and keep a-Lat the same between RFix LOP's? I've been operating under the belief that, as long as I use the appropriate latitude within Pub. 229, it doesn't matter if my a-Lat changes from RFix LOP #1 and LOP #2.
From: Parallel 47
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David Burch
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posted January 06, 2021 09:16 AM
#1)m there are three ways to advance an LOP. One is the standard method we teach in the book, from any place on the LOP1 mark off the DR track between LOSs and then move LOP1 to the end of that track, or 2) do the same thing for the Assumed position of the LOP and plot the LOP from that new AP, or finally you can use the method we call automatic advancement of an LOP where you compute an adjusted a-value based on the Zn and Course c and original a-value. This method is in both the HBS and in our textbook.
#2) There is no particular virtue of specific Lat or Lon when doing running fixes.
A nice nice trick to keep in mind if possible is take the first sunline on the beam, then you do not have to advance it at all for a running fix with the next sight you take an hour or two later.
From: Starpath, Seattle, WA
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