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I have a question about how a GPS calculates miles. Does it use a "true projection" like a map distance does, thus flattening out hills and valleys? Or does it calculate the actual distance traveled through the valleys and over the hills?
Around here the terrain is so flat that it would make little difference, but in northern GA's hills it could add up to a percent or two.
I know that there is 1.5 mile difference between my morning commute and the evening drive. How can that be when I start and end my trips at the same points? The answer is the highway interchanges that I go through. On my way to work I go through the inside curve and on the way home I have to go around the outside of the intersection. You wouldn't think such a little thing would make a difference, but we all know it's the little things that add up.
Just because your GPS and you odometer read different distances doesn't necessarily mean that either are wrong. They may be measuring different things.
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