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    Re: Lunar distance accuracy
    From: Alexandre Eremenko
    Date: 2007 Oct 27, 22:59 -0400

    > One of these days, clockwk.com is going to disappear,
    > Considering how carefully he has spelled out other
    I disagree with this. He even did not care to mention
    his scope power:-)
    And I continue to maintain that taking one shot per week
    with the purpose of investigation of lunars accuracy
    is ridiculous. All books on the lunars strongly insist
    on averaging at least 5 shots. And I suppose White read the
    books he cites.
    > In a follow-up post, you decided that
    > this wasn't so ridiculous after all,
    > and I agree with your logic there.
    There is a logic in not applying excentricity error.
    But this makes his results highly suspicious.
    Especially if we interpret them as single shots.
    > I propose that his arc error table would have read
    > something like this:
    > 30d: 0", 60d: +10", 90d: 0", 120d: -20". It should
    Highly improbable. Especially on a good sextant.
    See Simms theoretical formula for the arc error.
    By the way, one may conclude from the article that this
    very formula was used to determine his arc excentricity
    > "5. How Frank comes with the "mean error" of 0'.1, I don't know."
    > Take them in sets of four and average.
    Averaging observations taken a week or more apart
    has nothing to do with sea practice. Or even with
    land travel. It only makes sense when you determine
    longitude of a fixed observatory.
    > I found your point "6" amusing.
    > You seem to be saying that you don't trust
    > him because he writes plainly and without
    > pseudo-academic pretense. Oddly
    > enough, I like him for that.
    You misunderstood what I said.
    I did not say anything of the language. I was talking
    about the whole approach, "philosophy".
    There is one approach: to find what the truth is.
    For example, to evaluate the lunar method accuracy.
    And another approach: to convince people in something
    which you already know or believe.
    To promote some agenda.
    He seems to be using the second approach.
    I call the first approach "scientific".
    It has nothing to do with "language".
    > You know, they do have calm days on the oceans, Alex :-)
    Yes, they do. Have you seen
    www.math.purdue.edu/~eremenko/accuracy.html ?
    where the results of various observers are
    represented graphically?
    > That's Henry Halboth.
    > After getting a longitude accurate to within
    > 6 miles from a lunar distance
    I also have one or two lunars taken from sea with
    this accuracy. I even have a shot with a POCKET sextant
    from sea with this accuracy! I posted it 2 years ago.
    So what? I do not conclude from this that one can
    use a pocket sextant at sea to determine longitude
    within 6 miles:-)
    Henry, if by chance you are reading this,
    could you please tell us, how many times (perhaps in
    a certain definite period) did you make lunar
    observations at sea, and how many of those gave you
    longitude within 6 miles?
    > ...So that's ONE data point.
    Yes, exactly.
    > Finally, I would emphasize that lunars
    > were widely used in the early
    > nineteenth century --so they MUST
    > have been accurate "enough", whatever
    > "enough" means.
    For those British officials who made the longitude
    prize "enough" was 1/2 degree in longitude if I
    remember correctly.
    > There is ample evidence
    > for them in the logbooks.
    Evidence of WHAT? That lunars were widely practiced?
    Nobody seems to deny this.
    Or that "lunars can give you your position reliably
    to 6 or to 15 miles" ?
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