An octant was used to calculate a ship’s position on the earth using the mid-day sun. By drawing a triangle between the sun, the ship, and the horizon line sailors could estimate their ‘dead-reckoning’.
Printables:
Additional Links:
The Smithsonian provides an overview on using the octant for navigation at sea.
https://amhistory.si.edu/navigation/type.cfm?typeid=4
A tutorial for using the Octant.
https://www.youtube.com/watch?v=h0A_ue9DBmw
