Hi Dialmakers, A simple pair of pivots allows adjusting a dial for Longitude, EOT and daylight savings differences.
In this case we are talking about a horizontal dial with the standard gnomon replaced by a Virtual Gnomon, that is a vertical pin that, measured from dial center, subtends the Latitude angle and would touch the style. If that vertical pin is extended through the dial face by a small amount and rested on a pivot block that is one pivot of a Virtual Hinge. The second pivot is made by placing a vertical pin down below the dial face directly in line with the dial center, extending below the dial by the sum of the Virtual Gnomon height added to the small amount from above and resting on the second pivot block. This second pivot block can be outside the dial plinth allowing for movement. This longer pin should clear the plinth by enough to allow movement. The movement is curved and not in the plane of the vertical plinth face. This Virtual Hinge will allow the full sundial to rotate around an axis parallel to the earth's axis. Doing so will allow for longitude and seasonal adjustments in a simple fashion. Fixation of the dial face in a fixed position depends on the dial face and plinth shape and design. A similar pivot pair can be constructed for some vertical dials. Enjoy the Light! Edley.
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