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Old 08-07-2017, 01:47 PM   #8 (permalink)
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Civic DX (sold) - '97 Honda Civic DX
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Most cars have the speedometer show a slightly higher speed than actual, possibly to reduce the manufacturer's liability for speeding tickets. The odometer is usually much more accurate, though factors like different tires can change that. If you have your scangauge show speed, it'll probably be pretty close to what your GPS says. The car knows the actual speed and just has the speedometer show higher.

Does your GPS have any sort of trip odometer? If so, you can reset that and the car's trip odometer before going on a drive and compare the two at the end (preferably a long highway drive).
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