Oughtred invents universal equinoctial ring dial The two-ring universal equinoctial ring dial was invented by the English mathematician William Oughtred (b. 1574, d. 1660). It is described in his 1652 book on sundials. Unlike horizontal garden sundials, the equinoctial ring dial can be used in any latitude and is self-orienting, requiring no compass. At the Royal Museums Greenwich is an example (pictured here), created by the English mathematical instrument maker Elias Allen, that probably pre-dates this account. Its date of manufacture is around 1635. Allen was the first maker of universal equinoctial ring dials and was a friend of William Oughtred, their designer. Image Credit Universal equinoctial ring dial, Elias Allen, c1635. ID: AST0207 © National Maritime Museum, Greenwich, London, CC BY-NC-ND 3.0, Universal equinoctial ring dial | Royal Museums Greenwich
