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    Re: Lunar distance measurement in ideal conditions: attainable accuracy.
    From: Alexandre Eremenko
    Date: 2013 Jan 18, 11:02 -0800

    Dear Doug,

    There is still some profound mystery about my Lunars, which I practice for
    almost 10 years. Almost all observations are positively biased by about +0'3
    in the average. Why this happens, I do not understand at all.
    (This was discussed on the list many years ago, but no satisfactory
    explanation was ever given),
    The Index correction (which I frequently determine with all means at my disposal)
    is about -0'3, and stays constant since I bought this sextant, and I always apply it.
    The arc error was checked about 10 years ago by Freiberger and Cassens Plath
    (and I have 2 certificates issued by them).

    Frank once handled my sextant for a week or so, and found no systematic error.
    The only remaining explanation remains some sort of "irradiation" or
    even more mysterious "personal error".

    Indeed, I notices that if I use IC -0'6 (instead of -0'3 that I always find),
    then all my observations will be centered (=unbiased, zero average error,
    positive and negative errors equally likely).

    But this explanation is unsatisfactory for the following reason:
    I mostly observe Lunars. If I do something wrong when touching the Moon disc,
    then the errors of far limb and near limb must be of opposite sign.
    But they are of the SAME sign (always positive).

    It is the same for all range of angles, big or small, the amount of data I have
    is enormous.
    My experience with other sextants is small (for statistics) and It does not
    show any similar bias.

    I almost always overshoot any Lunar or star distances.
    And I have no plausible explanation why can this happen.

    Alex.

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