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    Backstaff experiments
    From: Lou deMartelly
    Date: 2017 Apr 10, 11:44 -0700

    I have been experimenting with the backstaff and have built several with changes in each.  In the process several questions have come up.  First, the scale on the large arc is an expansion of one of the steps on the small arc.  If the small arc is stepped at 15 deg. then the large arc need only be 15 deg. -- not 30 as all are shone and the instrument half as tall.  Second, if the aperture in the sun vane is 1/4" and round, the image on the sun vane will be round and sharp.  A 1/8" line above the horizon line (upper limb) will eliminate the half diameter correction.  Third, if the index pointer is marked, the arcs on Brahe's transversals can be eliminated.  Finally, a USCGS analemma will give reasonable declination and equation of time data for mid course tracking against a DR plot.  While the backstaff is not suitable at night most navigation is done in the daytime, and solar navigation is dramatically less complicated than celestial (night) navigation.

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