Universal equinoctial ring dial for all latitudes. This dial has the means for measuring the altitude and zenith distance of the sun, and is combined with a circular slide rule. It consists of three concentric rings and a bridge, folding flat when not in use. The outer ring slides against the meridian ring and is attached to a swivel ball stem, which is pierced by a suspension ring. The latitude indicator is a mark on the inner edge of the outermost ring, which also has an hour scale on its obverse side (probably for determining solar altitude and zenith distance). The meridian ring has a degree scale on both sides and the equinoctial ring has hour scales on both its obverse side and its inner-rim. The bridge carries a date scale on one side and an unfinished declination scale on the other. There is a crude sliding pinhole gnomon set between the bars of the bridge, which is adjustable for solar declination.

The main part of this instrument is an authentic 18th century dial with a circular slide rule included in the outer two rings. It appears that some of the scales may be later additions. The bridge, which is very poorly made, and the suspension ring are clearly 20th century replacements of lost originals.

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.