A Sextant is an instrument used to calculate global positioning in estimated navigation, but it can also be used in order to calculate distances based on the apparent size of objects. It is used to measure the angle between two objects, observing the horizon through its lunette and moving the alidade until the image of the object coincides with the horizon. A double reflection mechanism allows the user to reach a calculated angle value, which will be pointed in the alidade through the Sextant's limbo. Such angle measures usually have great accuracy.
Due to its enormous importance to navigation, the Sextant has been recognized as the symbol of maritime navigation for more than two centuries.