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    Re: Was this optical instrument designed for celestial navigation?
    From: Hewitt Schlereth
    Date: 2016 Feb 3, 13:42 -0800
    John, when you say "our nautical almanac" was it specific to your ship and especially to the place on the ship you took sights from?

    Dip is roughly the square root of how far in feet your eyes are above the surface of the sea. On a 40ft sailboat, dip is about -3 minutes of arc. On a ship, it can be -10 minutes of arc or more.

    Hewitt

    On Feb 3, 2016, at 10:24 AM, John Morris <NoReply_Morris@fer3.com> wrote:

    David, thanks.  I did celestial nav when I was X0/navigator of a USN ship, and got very tight 3, 4, or 5-star fixes.  I avoided planets because additional corrections were needed.  We were never taught about horizon dip.  Do you think that parameter was already figured into our nautical almanac, or is that figure one that can only be obtained locally at time of star observations?

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