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Mechanical equinoctial dial

This instrument is used to tell the time in the customary way for mechanical equinoctial dials, but the means of aligning it with the meridian is very unusual. Within the meridian ring is a moveable ring in which is a plate in the plane of the ecliptic. On this plate is an index-arm moving over a calendar scale. The index is set to the date and the position of the instrument and the ring adjusted until the index is directed towards the sun.

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