The folding sundial was made by the Nuremberg compass maker Jacob Karner, who was born in 1612. He married for the first time in 1634 and completed his master qualification roughly around then. This is indicated by the master mark "3" punched into the ivory at the bottom of the compass bowl and the manufacturer's abbreviation "IK", which stands for Jacob (Iacob) Karner, punched between the pin gnomon on the base plate.
The folding sundial's two ivory plates can be opened at a 90° angle and fixed with two hooks. The watch is then aligned in a north-south direction using the compass built into the base plate. Now the thread between the two plates stretches so that its shadow falls simultaneously on the vertical sundial's scale on the inside of the lid (Ib) and the horizontal sundial on the top of the base (lla). The vertical sundial displays the hours in Roman numerals (VI-XII-VI, with half-hour stars and quarter-hour points), which are "translated" by Arabic numerals (6-12-6) in the semicircle below the six-pointed star. The horizontal sundial displays the hours with Arabic numerals (4-12-8, with half-hour stars and quarter-hour points). Under the compass bowl there are two smaller sundials, whose shadows are indicated by the central pin gnomon: one for the Italian hours counted from sunset (9-23) and one for the Babylonian hours counted from sunrise (1-15).
Mareike Wöhler 2018
CC BY-SA 4.0