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    Re: Magnetic Variation. (has been: Magnetic Declination) Version 11
    From: Doug Royer
    Date: 2004 Feb 13, 13:57 -0800

    Thanks Keiran.
    I have a few questions concerning the below notations.
    1.Alt sun symbol  dd 30' ??? please explain
    2.I understand the haversine column.Where I get lost is:
    1/2 sum 62dd 30'
    diff    37dd 00'
            77dd 25'
    Please explain the above.
    Yes,do post other techniques.However,let's explore this one 1st so I
    understand it.
    The Australian explorer Augustus Gregory used several techniques for finding
    variation (i.e. difference between true and magnetic north. I will quote one
    here using an early morning sun altitude. This is verbatim from the field
    28 AUGUST 1856 at Camp LVII
    Alt sun symbol  dd 30'          az N 279dd 30' e mag
    Polar Distance          99dd 30'
    Lat                     18dd 00'           sec .021794
    Alt                      7dd 30'           sec .003731
                         2)125dd 00'
            1/2 sum         62dd 30'          cos 9.664406
            diff            37dd 00'          cos 9.902349
                            77dd 25'   log sin sq 9.592280
                           282dd 35'
                           279dd 30'
                             3dd 05'   var E
    So there you have it. Mag var with a compass, sextant and log tables. In
    this case he did not use amplitude tables. Also because he is on land with
    no ship nearby, deviation is presumed to be zero (I think). This was only
    one technique he used and is based using haversines for a solution of the
    celestial triangle originating at his visible pole i.e. the south pole.
    I can post some of his other techniques if you are interested..
    Kieran Kelly

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