Universal equinoctial ring dial, Johann Sommer

This fire gilded brass and silver ring dial is made and signed by Johann Sommer, Augsburg. The universal equinoctial ring consists of four parts: a suspension which can be adjusted according to the degree of latitude, a meridian ring with degrees of latitude from 0 to 85, a rotating equator ring with 24-hour indication (two times I-XII) and an engraved central bridge with a sliding lens. The ring dial can be used at different latitudes and is therefore referred to as universal. When in use, the correct latitude is first determined, with the aid of the indicated cities and latitudes on the meridian ring and the equator ring, after which the suspension is set to the right latitude. Then the equator ring is folded down and the movable lens of the central plate is set to the right month or constellation. The sun falls through the lens onto the hour ring and thus indicates the correct time.