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Equinoctial sundials

In an equinoctial sundial the hour ring is placed parallel to the equator. Sometimes the inclination of the hour ring is fixed but more often it can be altered, so that the dial can be adjusted to work at any latitude on the earth.

The simplest arrangement uses a rod at right angles to the hour ring to cast the sun's shadow [3]. The crescent dial [2] is a variant in which the hour ring is split into two opposed arcs. The toothed outer edge of the hour ring of [1] moves a small gear wheel connected to a pointer indicating minutes. New versions of the equinoctial dial were still being devised in the 19th century [4].

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