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    Re: MkIXa bubble sextant performance
    From: Jean-Philippe Planas
    Date: 2007 Apr 4, 22:41 -0700
    Hi Alex,
     
    Did you try to identify an Index error or any systematic error?
    Did you solve the issue of the bubble getting bigger during the observation after having been reduced when starting the observation session?

    alex <eremenko{at}MATH.PURDUE.EDU> wrote:

    After a month of practice, I can find my position within 2-3 miles
    with this sextant.
    The use of the averager gives better results than a single
    observation.
    But averaging 5 single observations by hand gives the same precision
    as the mechanical averager does (it averages 60 observations).

    Here is a typical complete fix with the averager:
    GMT April 3, 1:28:46 Sirius 28d22' ; 1:51:55 Venus 15d18'.5
    Using DR 40N, 87W, I obtain
    Alt of Sirius 28d44'.2, Azimuth 207d,
    Alt of Venus 15d12'.8, Azymuth 282d.
    Correcting for refraction and plotting on the Universal Plotting Sheet
    gives this position 40d20'.5N, 86d54d.5W, as read from the
    plot with 0'.5 resolution.
    My true position was 40d27'.2N, 86d55.8W,
    so the error is slightly more than 1 mile.

    In this reduction I used the Complete on Board Celestial Navigator,
    which is not very precise but very handy indeed.

    Here are two typical series of individual observations (averager off,
    reduced
    with the Almanac and computer).
    Venus, errors: 1'.8, -2'.4, -0'.9, -0'.2.
    Sirius, errors: 1'.2, 1'.7, 3'.0, 0'.0, 1'.8.

    Alex.



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