Muhammad b. Abi Bakr, Astrolabe, Isfahan, 13th century, American Museum of Natural History Library, The Bliss Collection, Photo: Kendra Meyers
This Persian astrolabe from the 13th century is believed to be the oldest working geared instrument in existence. These tools created a 2-D map of the sky and could be used to determine latitude. It was helpful in the Islamic world in determining the direction of Mecca. This astrolabe has a calendar on the back that shows the lunar phase and the position of the sun and the moon in relation to the zodiac signs.