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    Re: Problem with a sextant
    From: Alexandre Eremenko
    Date: 2006 Apr 25, 10:43 -0400

    Dear George,
    >Any error due to wear on the worm would be expected to repeat at
    >one-degree intervals, so could affect readings close
    Sounds very convincing!
    So it is the arc. Or...the arm pivot.
    > Why not really misadjust the index mirror, in a big way,
    > Ideally, one might wish to shift the zero by
    > perhaps two and a half degrees, to use an
    While I am experimenting, I found the following alternative.
    Instead of determining my IC
    by the usual procedure, using one star,
    I use TWO stars at a small distance.
    Yesterday I used Castor-Pollux distance for this purpose,
    which is 4d 30'.3
    (Nautical almanac does not have Castor;
    I had to use ISNO Astronomical almanach to compute this).
    I will post the details in a separate message,
    but from this Castor-Pollux procedure I found the index
    correction -0'.7. Such correction would make my all
    other star distances taken in the last week almost perfect!
    > It's a potential problem, that the older,
    > Vernier sextants didn't suffer from.
    > Another disadvantage of progress, perhaps?
    I also think so. And I hope my next sextant will be
    one of those old ones with Vernier and microscope
    and no teeth to worry about! If I find a good one.

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