A ring dial is for use in a fixed latitude, but the universal ring dial can be used over a wide range of latitudes. It consists of three rings and a strip with slider. A flat vertical brass ring, with grooved outer edge, fits within a ring of circular cross-section, and slides within it. The outer ring is suspended from a shackle or mounted on a foot. One side of the inner ring carries a scale of degrees, 0-90, for adjustment to latitude using an index on the outer ring. Pivoted within the inner ring is a further ring which can be swung out at right angles, carrying the hour scale. A diametral bar traverses the interior of this last ring; the bar has a slot in which a small piece with a pinhole slides. The slider moves along a scale of dates, or corresponding zodiacal signs. In use, the second ring is adjusted for latitude and the pinhole set to the date. The instrument is then rotated until the spot of light passing through the pinhole falls on the hour ring, where the time is read. The invention of the universal ring dial is attributed to William Oughtred (1575-1652). Dials incorporating these principles were manufactured by the London instrument maker Elias Allen in 1652.