I found the ODO in the X was just short of being exact to the GPS distance shown with new, full tread tires full inflation. It would click off a mile about 50ft B4 the GPS would. As the tires wore the 50ft distance has increased to well over 100ft per mile. That condition has shown itself in a overreading of distance on the ODO when compared to the GPS distance after a long trip.

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!