The mathematician, William Oughtred (1574-1660) is best known for his book "Clavis Mathematicae" published in 1631. In the second edition of his book "The Description and Use of the Double Horizontal Dyall" which appeared in 1652 there is an appendix "The Description of the General Horological Ring". It describes a portable ring dial that he invented earlier in his life and was based on the astronomical ring first described by Gemma Frisus early in the 16th century and the armillary sphere. Elias Allen had close connections with Oughtred and was advertised as the only maker of the universal equinoctail sundial at that time. It can be assumed that Allen was the first maker of this type on sundial that was to become popular through the second half of the 17th century and throughout the 18th century. The engraving by Wenceslaus Hollar showing Elias Allen seated at his workbench with a ring dial in the foreground dates from about 1640. The instrument is also depicted in Anthony Van Dyck's portrait of the Earl and Countess of Arundel painted in 1639 to celebrate the Earl's plans for an expedition to Madagascar. A similar dial in brass is in the collection of the National Maritime Museum, Greenwich. This example being made of silver would have been more expensive and might have been made on commission or as a presentation piece. See: Hester Higton "Sundials. An Illustrated History of Portable Dials", Philip Wilson, 2001. pp78-84.
An Important Elias Allen Universal Equinoctial Ring Dial, English, circa 1635,