This unusual instrument gives the time in Italian hours. The inscribed date 1586 was added several decades later in a different hand. The hour scale is marked only faintly in ink and has been partly rubbed away. The back of the instrument has a short explanation of the nocturnal's use.

Technical details:
Nocturnal for use with pointers of the Great Bear. Shaped handle with pivoted suspension piece.
Obverse: Pointer arm pivoted to the centre of the main disc.
Reverse: Unequal date scale divided anticlockwisw to named month, subdivided to one day. Month arcs most widely spaced for Jan & Feb, and shortest for Aug & Sept. Pointer has straight edge and two stars marked along it.
Reverse: Rotatable ring around circumference held by three brass lugs. Italian hours marked very faintly in ink on ring around inside edge.