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Users of Global Positioning System satellite navigation are bracing
themselves for the evening of 21 August, when the satellites鈥� date-counting
mechanisms 鈥渞oll over鈥�. GPS satellites count dates in weeks, starting with the
first week in 1980, but only count up to 1023. After that, the counter rolls
back to 0000, which might prevent some civilian GPS receivers from interpreting
the signals.