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kalleboo
on March 14, 2015
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Train doors require GPS signal to open despite sta...
Or an odometer (wheel revolutions) which is what buses often use and the technology is over 2000 years old[0] and quite cheap and reliable
[0]
http://en.wikipedia.org/wiki/Odometer#Classical_Era
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[0] http://en.wikipedia.org/wiki/Odometer#Classical_Era