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    Re: Increased dip for "Nearer" Horizon or Level Line
    From: Richard M Pisko
    Date: 2011 Jul 26, 00:18 -0600

    On Mon, 25 Jul 2011 21:22:40 -0600, Bruce J. Pennino
    > Second question: I have a laser level, high quality Nikon construction
    > level, and a surveyor's total station.  The total station has an
    > internal scale that I can estimate a vertical angle to plus or minus
    > about 2.5 seconds. Can I use these instruments to establish horizontal
    > lines on  a wall?
    Make it a wall (or feature of a building) far, far away.  In 100 yards,
    roughly a city block, an error of one inch in vertical positioning of your
    head and sextant would give an error of one minute of angle.  So a one
    inch error in 2500 yards would be about your total station's accuracy
    limit.  At that distance, you would also have to take the curvature of the
    earth into consideration to determine a "level", equipotential, or free
    water surface elevation equivalent to your eye height.
    The sextant at sea, when using the horizon as a reference, does not really
    use the level line, tangent to the earth's surface, as used in ordinary
    plane surveying.  Depending on the total station, you may be able to punch
    in distance and temperature, and account for curvature and refraction . .
    . I don't know for sure, but I think that would be your largest source of
    Richard . . .
    Using Opera since the"Dog" died

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