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    Re: "Attainment of Precision" article (1964)
    From: Thomas Kleemann
    Date: 2009 Jul 08, 23:58 +0200

    Nicol�s de Hilster schrieb:
    > frankreed{at}HistoricalAtlas.com wrote:
    >> If you want a really good value for IC, shoot the Sun or the Moon 
    limb-to-limb ... it's usually more effective than the standard sea horizon 
    test (but the standard test is usually quite sufficient and it's the one that 
    should always be taught).
    > And can you explain how this is done? 
    You shoot a set of two sextant readings, where the double reflected sun 
    and the directly observed one are showing an eight-like figure with 
    their touching limbs. After the first shoot you exchange the two images, 
    so that the lower becomes the higher and vice versa.
    Now you have got two readings - one on the arc and one off the arc,
    e.g. 31' on, 32' off.
    - substract them and the index error is half the difference (-0.5' in 
    the above example)
    - add them and divide by four will get you the semidiameter (15.75'),
    which you can compare to the almanach to check the precision of your 
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