Sundial Diptych, solar watch, diptych desk sundial handmade astronomy navigation gnomonic

Reproduction of an antique travel sundial (Ars longa diptych), in mahogany wood.
Instructions for use:

By opening the sundial to 90°, the compass needle is oriented towards the north. The shadow cast by the thread on the dial will indicate solar time. When the upper dial has a sliding scale, the time can be determined at any latitude, the lead serves to verify that one is on a horizontal plane.
(there will be an explanation of how it works inside the package)

The sundial is the oldest time-measuring instrument ever discovered. The term “sundial” indicates that type of sundial that indicates only midday, that is, it indicates when the Sun is above the local meridian.
These instruments were already known in ancient Egypt, among the Greeks and Romans, but the origin of this science is even older and the first evidence dates back to the Neolithic.
In its minimal form it consisted of a prop planted in the ground, in the traditional form of a stylus called a gnomon, which projected its shadow on a horizontal or vertical surface, called a quadrant, indicating the astronomical time.

The Nuremberg Diptych is a portable sundial, which saw its diffusion in the 17th and 18th centuries in Germany, through the production of many examples, in wood, ivory and other materials, especially in Nuremberg where several families of gnomonist craftsmen resided.
The diptych consists of a rectangular box with a book-like opening, equipped with a compass inserted in the base to orient the instrument in a north-south direction.
The hour indicator is made of a wire that is tensioned when the lid of the box is opened and is equivalent to the well-known polar stylus. The wire in many models can be moved at its upper attachment point, so as to allow the instrument to be used for more latitudes.
On the horizontal side, where the compass is inserted in the central position, there are usually circular or hexagonal time dials, while a similar one is often, but not always, present on the vertical side.
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