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Thread: 1714 portable compass dial - photo

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    mklotz (Apr 20, 2021)

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    It's more likely a portable equatorial sundial. The fact that the hour markers are spaced uniformly on the pierced plate confirms its equatorial nature.

    The compass embedded in the base is used to get the tilt axis of the pierced plate pointing E-W. Then the pierced plate is elevated to an angle matching the latitude of the observer. Then the arm is turned until the sunbeam from the small hole in the vertical falls on the pointer in the middle of the small circle. When this happens, the arm is pointing to the time engraved in Roman numerals on the circumference of the pierced plate.

    The use of the small circle and its pointer escapes me. I've never seen one with such a device.
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    Regards, Marv


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