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    Re: micrometer sextants.
    From: Alexandre Eremenko
    Date: 2007 Nov 8, 16:01 -0500

    On Thu, 8 Nov 2007, [iso-8859-1] Wolfgang K�berer wrote:
    > Even in the Plath patent description of 1921 the
    > vernier is described as being more accurate,
    > it says that the micrometer has
    > been added to be able to get a quick
    > reading when no high accuracy is
    > required.
    And perhaps Plath was right. I suppose that vernier IS
    more accurate, and has fewer week points (backlash,
    sea salt ang bugs coming between the teeth and the screw).
    It seems that conservative seamen opposed this innovation
    (reading the minutes on a drum) and I remember reading
    an argument
    of some author who tried to convince them that micrometer
    is better by the following argument:
    reading of micrometer is so much faster that you can
    take 3-4 sights with a micrometer in the time required
    for one sight with vernier.
    By averaging 3-4 sights intstead of one, you achieve
    better precision.
    Unfortunately, I don't remember where I read this.
    P.S. I had a vernier C. Plath, and my experience
    confirms that reading a 10" vernier scale is a real
    pain, especially in poor light, and it indeed takes 4-5
    times longer than reading a micrometer drum.
    But the main disadvantage of the two old (XIX cent) sextants
    I tried was the very poor quality of their telescopes,
    incomparable with the modern inverting scopes.
    In addition to this, my XIX century C. Plath had a very
    non-rigid frame, so after some trial shots, I sold it.
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