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    Re: Freiberger sextant
    From: James N Wilson
    Date: 2012 Aug 13, 14:49 -0700
    I agree wholeheartedly. You've stated the case very clearly. I would bet that if you applied your test with a sextant with a vernier, you would get the same results!
    I'll repeat myself, noting that with the vernier you have the opportunity to read from its wrong end, introducing an eleven minute error. A big price to pay for an almost nonexistent increase in accuracy.
    Maybe I should clarify. Without a vernier, there is only a single index mark, impossible to mistake, where with a vernier the user has two choices. One is more obvious, but I wouldn't take note of this if it hadn't happened. Once is too often. Verniers are worse than nothing.
    Jim Wilson
    On Mon, 13 Aug 2012 17:08:07 -0400 Ridge White <whiteinstruments@gmail.com> writes:
    Hi Jeremy,

    You mentioned wishing your Freiberger could be read to .1', a tenth of a minute. 

    In our many years of selling and servicing sextants of many types, we are often asked about the desirability of a vernier scale - instead of just an index mark - opposite the micrometer. A number of times I have pulled from our display a sextant without a vernier scale and have arbitrarily turned the micrometer drum to some position, at which time I ask the customer to read the micrometer drum against the index mark. Three times out of four the customer and I agree. When we don't, we differ by one tenth of a minute. Interpolating is something we do all the time.

    Given the likelihood that no sextant can repeat a reading down to one tenth of a minute because of tiny amounts of "slop" between the tangent screw and the limb, vernier scales strike us as maybe desirable - but by no means necessary - for accuracy. 

    Just one man's opinion. Anyone else have thoughts on this?

    Ridge White
    Robert E. White Instruments
    PO Box 775
    Medfield, MA 02052

    Tel: 617-482-8460
    Fax: 617-482-8304

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