The introduction of the octant, which reduced the determination of the ship's position to a simple measurement of angles by reflection, represented an innovation and an improvement of great importance in navigational instruments with respect to sextants, nautical astrolabes and others of the kind used previously.
Indeed, in the octant the sun's image reaches the observer's eye after being successively reflected by two mirrors; on the fixed mirror it is possible to see at the same time the horizon and the image of the twice-reflected sun; consequently a star, brought to the horizon by reflection, can be kept there not only on land but also on a ship in movement.
Although the sextant, which was more precise, had been introduced in 1770, the octant, owing to its low price, was used up to the end of the 19th century and in the first years of the 20th.