It is obvious.  The earth is not flat. The mile markers are in a straight
line, but  your bus must traverse the surface of a sphere, aka The Earth.
The variance is because of valleys (high correlation) and hills (low
correlation).

-Matthew

Matthew Pollard          "Racing with the wind and flirting with death
Dept. Of Chemistry        So have a cup of coffee and catch your breath"
University of Idaho
www.uidaho.edu/~poll7356

>
> Here's what I recorded
>     my trip odo             I-70 milepost
>        77.8                      0
>       186.2                    100
>       292.0                    200
>       323.0                    230 (Colorado state line)
>