#Astronomy
This is the "Planétaire ou planisphère nouveau" by M. Flécheux (1780).
A paper (or cardboard) astronomical instrument, with which you can derive some astronomical parameters.
Background: a star chart and a calendar, a pivoting ruler carrying scales and a set of 3 rotating wheels.

Knowing the date, longitude and local time, you can find the time of passage of stars or Moon at the meridian. Inversely you can derive your longitude by the time of meridian passage. Flécheux claims that his instrument is a solution to the longitude problem at sea, if you carry a watch with the time of the home port... quite a bold statement, given the modest size of the hour wheel, but certainly a major question of his time. In 1780 only a few marine chronometers were available.

Otherwise a pretty instrument. To understand how it works, I couldn't help making a modern reproduction ( #TeXLaTeX and #python).
The original (perhaps unique extant copy?) is sold 20000 GBP in London...