In almost every account of the mystery surrounding the Bermuda Triangle, you'll see reference to the fact that it is one of only two places on Earth (the other being the Devil's Sea off the coast of Japan) where a compass points to true north rather than magnetic north. Theorists say that this causes compasses to malfunction and ships and planes to get off-course [source: Mayell].
A compass works because its magnetic needle is attracted by the magnetism of Earth, which draws it to point to the constantly shifting Magnetic North pole. The Geographic North pole, on the other hand, is static and is located 1,200 miles (1,931 kilometers) north of the Magnetic pole. The variation between the two readings is known as magnetic declination (or compass variation), which can change as you move across the globe [sources: Government of Canada, USGS ].
The agonic line is an imaginary line where true north and magnetic north are in perfect alignment — there is no magnetic declination. At points west of the agonic line, a magnetic needle will point east of true north (positive declination). At points east of the agonic line, a magnetic needle will point west of true north (negative declination). Extended lines that mark the constant magnetic declination away from the agonic line are called isogonic lines [source: USGS]. In the early 18th century, Edmund Halley noticed that the agonic line was slowly moving westward. He came up with the idea of showing declination as contour lines on a map [source: Gubbins and Herrero-Bervera]. Since then, scientists have noted a westward drift of the agonic line with an average velocity of about 0.2 degrees per year. The drift is not equal in all places, however. It is stronger in the Atlantic than in the Pacific [source: Government of Canada].
Navigators must always compensate for magnetic declination when charting their courses. While the agonic line once passed through the Bermuda Triangle, it now falls within the Gulf of Mexico, rendering claims that it can contribute to disappearances in the Triangle inaccurate. Calculation errors anywhere could cause a plane or ship to go off-course. The compass malfunction theory assumes that experienced pilots and captains passing through the area were unaware of magnetic declination, which is unlikely. Not to mention that the vast majority of boaters and fliers pass through this area without incident [source: Britannica].