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    Magnetic Variation?
    From: Doug Royer
    Date: 2004 Feb 12, 13:41 -0800

    Thank you George for the background info.I didn't know that at one time
    people were trying to determine longitude useing mag. var.
    After reading your post I have a few questions/comments about what you
    wrote.Perhaps I missunderstand what you were saying.Bear with me as I try to
    understand.
    In my training and experiance one uses amplitudes to find the compass
    error.By adding or subtracting the variation one finds the compass deviation
    at that heading and time.With out knowing the deviation how can one know the
    variation useing amplitudes?In your explaination is the sight taker useing a
    hand held bearing compass or a sight vane on the ship's compass or
    repeater?There could be a differance because if one is useing a hand held
    compass to observe the amplitude one doesn't take deviation into account as
    one does on the gyro or ship's compass's sight vanes.
    Let's tackle amplitudes 1st.I know of 2 ways one can find an amplitude of a
    body.By observing the body's amplitude on the visible or celestial horizon
    with a compass and useing the amplitude tables or by calculateing the body's
    amplitude on the visible or celestial horizon.
    In either precedure above the resulting amplitude is compared to the
    observed amplitude thus finding the compass error.
    Keiran stated he has a way to find local variation useing " a
    sextant,compass and amplitude".How can this be done?Am I missing something
    or are my thoughts to confined ie. ship board application only?
    
    
    

       
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