Navigation instruments are tools used by sailors and navigators to measure the angle between two objects in order to determine their position. The sextant is a navigation instrument that measures the angle between two objects, such as the horizon and the sun or stars, to calculate the latitude of a ship. It was invented in 1730 and is still used today. The octant is a similar instrument that was invented in 1731 and is also still used today. It measures the angle between two objects, such as the horizon and the sun or stars, to calculate the longitude of a ship.