As a curiosity, two weeks ago I began the studies to obtain the private pilot licence (a true dream come true for me). Today (I must assist to weekend classes), one of our instructors mentioned that the United States reduces the precision of the information supplied by their satellites for security and military reasons. Some GPS equipments, while the last war in Iraq, gave erroneous position readings of about 400m. It seems that it depends of each equipment. Some of them, specially some models mounted in cars, can correct such errors using "alternative ways", based in the known speed and an internal electronic compass.
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