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    Re: Agnostic gnomon and horary error
    From: Chuck Varney
    Date: 2024 Jun 3, 16:53 -0700

    Robin Stuart,

    Good work on using two of the armillary rings to calculate the camera position.  I estimate that a photo taken at the same observer height and distance as in the Sundials cover photo, but with the 6.5 degree deviation from E-W that you calculated reduced to 0 degrees, would reduce the photo-measured gnomon angle by about 0.2 degrees--whether using your measured gnomon angle or Frank's.

    Regarding this comment to me in your first post: “Unfortunately I don't think the method you propose will work in practice.”  The method I proposed in that post was to make physical measurements of the meridian ring inside diameter and along its inner surface.  My closing statement (“Using the above information you can just look at the marked armillary sphere photo and see that the yellow-blue distance is greater than the yellow-white distance, which is wrong for a gnomon altitude that should be well under 45 degrees.“), as stated, applied to the subject photograph.

    Chuck V.

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