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    Re: One-body fix
    From: George Huxtable
    Date: 2009 Apr 27, 15:58 +0100

    Peter Hakel asked-
    "Nevertheless, I would like to know just how accurately one can measure
    azimuth in the field/ocean and what portable devices (besides compasses),
    are available for this (if any)."
    Even under benign conditions, I wouldn't trust any compass on a small
    vessel, carefully corrected as necessary for variation and deviation, to
    indicate true North as a reference to any better than one degree either way.
    I can't say whether the gyro-compass on a big ship would do much better than
    that (but rather doubt it...).
    I doubt if Peter Hakel's suggestion of navigating by altitude and azimuth of
    a body has much potential. Geoffrey Kolbe has pointed out some pitfalls
    already. For each degree, measured down from the zenith, of a body, an
    uncertainty of 1 degree in azimuth would give rise to an error in deduced
    position of about a mile, roughly speaking. From that point of view, high
    altitudes would be better. However, it's only possible to assess the azimuth
    of bodies near the horizon with any accuracy. Higher altitudes would call
    for a sighting device on a stabilised mounting, which was kept accurately
    horizontal. Such a platform might exist on a big ship, however.
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