# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Clarification offered and requested Re: Multi-Moon line exercise in 2 parts
From: Peter Hakel
Date: 2009 Aug 9, 16:33 -0700
Antoine,

From: "NavList@fer3.com" <NavList@fer3.com>
To: NavList@fer3.com
Sent: Sunday, August 9, 2009 2:07:31 PM
Subject: [NavList 9452] Re: Clarification offered and requested Re: Multi-Moon line exercise in 2 parts

> Second,
> Peter please be so kind as to confirm that you did process all the 33 shots of the "Moon near LAN" file, and only these ones.

Yes, that is correct, all 33 and nothing else.  In the other case (away from LAM) I skipped the second measurement, so there I only used 29 moonlines.

> Last but not least :
>    **** for those of us who use a "parabolic fitting" type of software, I would surmise that your software first identifies culmination time and height, from the
> curve shape, and then computes LAM as well as associated Height at time of LAM. Please be so kind as to indicate time elapsed in seconds between
> Culmination Time and LAM time. I get 2.9 seconds for this result.

Please, see my posting #9079 from July 11, 2009, in which I describe in detail how my "parabolic-fit" spreadsheet works.  It was originally designed for the noon Sun; which I then adapted for Jeremy's LAM case.  It does not calculate any uncertainties, nor does it distinguish between transit and culmination.  Instead, it prorates all altitudes to a common parallel of latitude (accounting for both the motion of the vessel and Moon's declination change) before fitting the resulting fictitious "noon" curve. In this mathematical scheme, meridian transit = culmination.

>    ***** when running Marcq Saint Hilaire method on 33 running fixes using Oberved position at LAM as DR position, I am getting back exactly to the
> same result within 0.1 NM (while giving all 33 observations exactly the same weight ). I would therefore think that, all your 33 data having been
> processed by 2 entirely different mathematical approach, this would somewhat reduce the risk of error since in both cases I get the same results.

I was happy to see my "LAM spreadsheet" and the "rapid-fire fix program" give essentially the same fix that also agrees well with your and Jeremy's results. This is why I am wondering whether I made a mistake somewhere in calculating the standard deviation for longitude.  Sometimes our results are better than we think they are - and this may be one of those times.

Peter Hakel

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