It is a pocket sundial that indicates the local time based on the position of the sun on each date of the calendar.
When the sundial is opened horizontally, it is rotated until the compass needle is north of the wind rose, and the shadow of the string is read on the dial.
This type of sundial was invented around 1640.
Nuremberg, Germany.
Late 18th century.
Ex-collection:
Mario Crijns, Oosterhout.