For centuries man has relied on the compass to navigate his course in the world. The early forms of a compass were merely magnetized iron ore on something that floated. A compass is a device that is sensitive to the earth's magnetic field and will indicate the direction of magnetic North for the user. In the 1930s, a Swedish innovator developed the modern day liquid filled compass. The modern compass types available such as the baseplate or map compass, sighting or lensatic compass, can be used alone or with GPS for a wide variety of uses from military, navigation, and geology, to survey and construction.