Original sentence: A prediction of the current magnetic declination for a given location (based on a world-wide empirical model of the deep flows described above) can also be obtained on-line from a web page operated by the National Geophysical Data Center, a division of the National Oceanic and Atmospheric Administration of the United States.In most areas, the spatial variation reflects the irregularities of the flows deep in the earth; in some areas, deposits of iron ore or magnetite in the earth's crust may contribute strongly to the declination.The magnetic declination (also known as grid magnetic angle in military circles, if the grid is aligned to true north) at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north.There are also three types of bearings--true, magnetic, and compass--which are related by the rules:
Edited sentence: A prediction of the current magnetic declination for a given location (based on a worldwide empirical model of the deep flows described above) can also be obtained on-line from a web page operated by the National Geophysical Data Center, a division of the National Oceanic and Atmospheric Administration of the United States.In most areas, the spatial variation reflects the irregularities of the flows deep in the earth; in some areas, deposits of iron ore or magnetite in the Earth's crust may contribute strongly to the declination.The magnetic declination (also known as grid magnetic angle in military circles, if the grid is aligned to true north) at any point on the Earth is the angle between the local magnetic field—the direction the north end of a compass points—and true north.There are also three types of bearings—true, magnetic, and compass—which are related by the rules: