Regarding the iphone compass article there is a mistake in the definition of Longitude.
longitude is the distance east or west of the equator.Lines of longitude are imaginary lines that divide the Earth.
They run north to south from pole to pole, but they measure the distance east or west.
The prime meridian, which runs through Greenwich, England, has a longitude of 0 degrees.
It divides the Earth into the eastern and western hemispheres.Your article was great at describing how the iphone works.
