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    Re: Navy MK 5 Octant Using Natural Horizon
    From: Greg Rudzinski
    Date: 2012 May 1, 12:10 -0700

    Alex,

    Spread or scatter has been used here on the list to describe the difference between maximum and minimum values. Not sure what the statistics term is (variance ?).

    On preset observations the micrometer is set exactly on an even minute of arc then the time is mark when the Sun's lower limb touches the horizon (fingers are off the micrometer).

    On normal observations the Sun's lower limb is dropped down to touch the horizon then time is marked (fingers are on the micrometer). The micrometer drum is then read to the nearest minute of arc which requires visual interpolation because the reading will appear somewhere between two even minutes of arc.

    Greg Rudzinski


    [NavList] Re: Navy MK 5 Octant Using Natural Horizon
    From: Alexandre Eremenko
    Date: 1 May 2012 13:43
    Greg,

    I am still somewhat puzzled how could you obtain 0.1' error
    from an octant whose scale is reading 2'.
    May I ask you few more questions about the procedure:

    a) what do you exactly mean by "spread"?
    The difference between two extremes? Or the standard deviation
    (=sqrt of the average of the squares of errors)?

    b) to what precision do you interpolate when you read the scale?
    I have not seen the scale but depending on the size of divisions
    one can interpolate such scale from 0.2' to 1'.
    What was exactly your procedure: how many digits after the dot
    your row data have?

    If your spread is the difference of two extremes then I
    do not see how could you possibly obtain such a numbers as 2.1'
    or 2.7' It is also hard to imagine that you can interpolate by eye
    to 1/20-s part of the scale division.

    Or perhaps you will care to type your raw data?

    Alex.

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