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    Re: Calibrating a sextant scale
    From: Alexandre Eremenko
    Date: 2007 Nov 25, 12:45 -0500

    Dear Frank,
    You wrote:
    > Using lunars, I made an arc
    > error table that had a maximum value
    > of 1.8 minutes of arc.
    and then:
    > eccentricity problem amounting to
    > as much as 0.8 minutes of arc.
    Of course, there would be no difficulty to detect such
    large errors using either Lunars or stars distances.
    By the way, this shows that the
    sextants you experimented with
    were of poor quality.
    The arc error of a good sextant is not supposed to change
    by 1'8 even if you ship it or transport in a car, is it?
    When, answering George's question, I said that
    "I failed", I was talking about STAR-STAR distances
    only. Which are less precise than the Lunars.
    My Sun- and Jupiter- Lunars
    (taken in long series and averaged) generally
    agree with the most recent certificate I have within
    0'2. As you can see from the statistics I posted on
    my web site. Determining the arc correction from Lunars
    is a long-term enterprize, this cannot be done in one night.
    So this procedure would be pretty useless in practice,
    if the arc error changes during a car transportation.
    Fortunately, in my sextant it does not seem to change:
    I transported it a lot by cars, trains and airplanes
    (in the luggage). Even IC does
    not seem to change much. It is between -0.3 and -0.5
    since I bought it.
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