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    Re: Sextant Accuracy from new member
    From: dpstephen
    Date: 2003 Mar 18, 09:35 -0700

    Hello all,
    I have been lurking for a long time here and will finally participate. I do
    a fair amount of celestial nav stuff, almost all from land. Use an Astra
    IIIb, pocket sextant, liquid and mirror artificial horizons and theodolites
    (Wild T-2, old K&E Paragon and Kern DKM-1). At my high elevation barometric
    pressure can have a significant influence on refraction but another large
    influence here is deflection of the vertical. I understand this can be as
    large as about 1' and where I live causes an E-W error of 29" and a north
    south error of 1". I live right on the edge of the rocky mountains thus the
    large deflection. As I understand it, if I did everything perfectly,
    observation, refraction, parallax (if needed), augmentation (if needed),
    calculations, perfect tables,... I would still be off by 29" (about 2900
    feet) due to deflection of the vertical. With the Wild T-2 theodolite
    (measures to 1") the readings I get are consistently about 1/2 mile in error
    to the east but quite a bit better north and south. With the T-2 the big
    deal is trying to get a really accurate time. There are free programs on the
    internet that will allow you to calculate the deflection at any location.
    Doug Stephen
    ----- Original Message -----
    From: "Fred Hebard" 
    Sent: Monday, March 17, 2003 9:12 PM
    Subject: Re: Sextant Accuracy
    > I don't know that I'm not too upset by recent war-precipitating events
    > to respond well, but here goes.  Perhaps we can find rational refuge in
    > our abstruse meanderings about an _almost_ obsolete technology.
    > It was very gratifying to hear from our professional sea officer, Doug
    > Royer.  I might imagine that my attempt to get as accurate as possible
    > is related to his comments about real-world conditions.  I also wonder
    > how close the winner of one of those jackpots generally was to the GPS
    > position?  I recall our correspondent from the arctic saying his shots
    > were within 0.2', and Bowditch saying that an experienced observer
    > could shoot to 0.1'.  I doubt I'll ever get to the level of experience
    > to which Bowditch refers, which I would expect comes from taking rounds
    > of shots five times a day or more.

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