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    Re: Noon Sun sights, Jamestown RI, this Sunday, Aug. 25
    From: Robin Stuart
    Date: 2013 Sep 12, 15:48 -0700

    Antoine,

    Glad you took the opportunity to crunch the numbers.

    You noted:
    " The most significant one concerns the Combined Height Correction most probably because of a slightly different dip value used in my computations. I have used combined values (computed for each observation) very close to 10.0' , vs. your +10.1' fixed value."

    I agree with you that +10.0' is a more standard value for the combined corrections and you correctly deduced that the difference lies in the dip. Since most of my sights are done using an artificial horizon it's typically not something I have paid much attention to. Thank you for pointing this out.

    You also said:
    "I also accurately compute ΔT culmination-transit and I find its value equal to 9.2s (vs. your 9.6s determination) It makes sense since you probably used the classical 1st order Formula:"

    I did use the first order formula but the difference appears to come from the number of significant digits included in d/dt Dec ['/hour]. I took d = -0.9 which was lifted from the Nautical Almanac. If instead d = -0.866 is used the first order formula gives 9.2s.

    You said:
    " the 1σ Latitude error is 0.4' vs. what would seem a significantly (much) higher 1σ value of yours."

    Using the full set of 14 observations the standard deviation in the intercepts is indeed 0.4'. For the purposes of the Monte Carlo I used the standard deviation of 13 observations (outlier excluded) which is 0.26' when truncated at 2 digits.

    You noted:
    " It might be questionable to reject the first observation as a definite outlier."

    My identification of the first observation as an outlier hinges on the fact that I know what my true location is and can compute the intercepts. Without that information I think that it would be difficult to justify discarding it. As my objective was to see how well one can determine longitude in a close to best case scenario and so I wanted to start with an uncontaminated data set.

    Regards,

    Robin Stuart

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