Instruments · a Light

An astrolabe is a model of the sky you hold

You sight a star or the sun through the bar on the back of an astrolabe, read its height above the horizon off the rim, turn the openwork grid on the front until it matches, and the instrument tells you the time of day or night, the direction you are facing, where any other star has got to, and the height of the tower across the street. No arithmetic is needed. The flattening of the sphere onto a disc is Greek geometry and goes back to Hipparchus. Muslim makers turned it into a standard object made in quantity, with prayer times and the direction of Makkah engraved on it. Chaucer wrote a manual for one in English, for his ten year old son.

Oldest dated example by Nastulus · 927 CE