early 18th century, English, with hinged strut, finely engraved with a full set of scales in the English pattern, with a long Gunter's scale 0-10-10-3,  the addition of sundial-making scales, (latitudes, hours, inclination of meridians and the related scale of chords), outer edge with 12" scale; Note: Clifton gives Saunders working dates as 1708-1743.