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    Re: What should I expect for a land based sight accuracy
    From: Alan S
    Date: 2014 Jan 9, 15:47 -0800

    Greg:

    Regarding accuracy of "land locked sextant shots",my own experience might be illustrative of what can be expected, though possibly not.

    I'm using an Astra 111B, with the factory telescope, 3.5 x 40mm and a Davis Artificial Horizon, essentially a dish of water, with sun and wind shields.

    I do AM and PM sun shots, 4 -5 hours apart, in the parking area of the apartment complex where we reside, and compare my calculated position fix with GPS coordinates.

    My calculated fix is usually inside 3 NM, sometimes inside 2 NM of GPS coordinates, sextant sights having been reduced and the LOP's plotted. I use USPS Sight Reduction Form and their CLS plotting sheet, which covers 1 degree lat x 1 degree long. Since I'm standing in essentially the same place for the sextant shots, the limitations of the CLS plotting sheet are not a problem.

    Looking at one such plot,the "a" distance for AM shot was 0.6 NM Away, PM "a" distance was 1.7 NM Toward. Plotting the LOP's gave me a calculated fix 1.8 NM, scaled with dividers, South-West of GPS coordinates.

    Hope the foregoing is of some help to you.

    Alan
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