A compass (or mariner compass) is a navigational instrument for fining directions on the Earth. It consists of a magnetized pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The face of the compass generally highlights the cardinal points of north, south, east and west. The compass greatly improved maritime trade by making travel safer and more efficient. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude). It thus provides a much improved navigational capability, that has only been recently supplanted by modern devices such as the gyrocompass and the Global Positioning System (GPS).