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    Re: Sight Reduction Formula Question
    From: Trevor Kenchington
    Date: 2005 Jan 8, 14:51 -0400

    Could someone either explain how the expressions for the sine, cosine
    and tangent of Z (as discussed on this thread) are derived or else point
    me to a published explanation? I have been trying to equate the three
    expressions but the trig I was taught as a 16 year-old is far too rusty
    for me to make sense of them. Nor can I find an explanation in any of
    the texts I have to hand.
    Any guesses as to why each textbook seemingly offers only one way of
    calculating Z? Any observer must be well aware of whether each of his
    sights is close to his meridian or to his prime vertical. So why are we
    not told to find Z from its cosine when the body lies to east or west
    and from its sine when it lies north or south? That way, ambiguities
    would be avoided and we would be working with trigonometric values which
    change swiftly with changing azimuth. (And without the complications of
    "ATAN2" calculator buttons or other ways of applying George's tangent
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                          Science Serving the Fisheries

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