杏吧原创

The Global Positioning System (GPS)鈥攁 fleet of satellites that allows
users to determine their position on the Earth鈥檚 surface鈥攚ill become 10
times as accurate in 2006, thanks to President Bill Clinton鈥檚 decision this week
to switch off a built-in error signal, called selective availability. SA was
introduced to prevent foreign powers getting the same positioning accuracy as
the US military, but now the Pentagon can switch SA on and off over particular
regions. With SA switched off, GPS will locate your position to within 20
metres.