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Rick,
what I meant wasn't to put 12 LOP's on the sheet, nor the bisectors to which
I referred were the ones between +2' and -2' couples of LOPs. The bisectors
were those between opposite LOP's which are meant to eliminate (or at least
reduce) systematic errors. I simply plotted the first 4 lOP's (index
correction -2') on a sheet and the others (index correction +2') on another
sheet and found out that the fix was essentially the same.
I agree anyway that handling the "index affaire" in the correct way is
indeed the best option...
Federico

-----Messaggio originale-----
Da: NavList@fer3.com [mailto:NavList@fer3.com] Per conto di
Richard B. Emerson
Inviato: luned� 18 agosto 2008 5.12
A: NavList@fer3.com
Oggetto: [NavList 6153] Re: Ocean Yachtmaster Exercises


First things first, I was wrong in my comments about moving LOP's by the 
amount of the index error or index correction.  Nonetheless, the concept 
raised a major "Not A Good Thing" flag when I read the first post in 
this topic.  And now I remember / understand why.  It's one of those 
things that is best be described as "right for all the wrong reasons". 

Can the LOP's be tweaked by the amount of the index error with opposite 
signs (in this case 4.0' or 4.0 nm)?  Running through the reductions 
with both Ic's shows the answer fast enough - so much for the "right" 
part.  Split the difference and there are the error-free LOP's.  But at 
the same time, the plotting sheet starts to look pretty ratty as (in 
this case) four LOP's become a total of 12 LOP's, six of which are in 
error.  And this is the "for all the wrong reasons" part.  What's on the 
sheet should be clear, as accurate as possible, and presented in such a 
manner that a complete stranger could read the story, presented on the 
sheet, without having to ask the author, "why is this here and what is 
that doing over there?".  Fudging LOP's after remembering there was an 
error in handling index error during reductions is a (IMHO large) step 
away from clarity.  It also opens the door for more error; are all LOP's 
"fudged", were some right and moved by mistake, or... the room for 
Murphy's Law expands a little too readily.  So I'll amend my summary 
comment to "You just shouldn't do it". 


Rick Emerson
S/V One With The Wind




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