Google "richardson effect", or check out http://en.wikipedia.org/wiki/How_Lon...onal_Dimension

Or, imagine you're running, and your body bobs up and down 4cm each stride. After an hour at a cadence of 85, you've gone up and down 5100 times, or 20,400cm. Thats 600ft of elevation gain and loss. Now, does that count? Applied to cycling, imagine bumps in the road, 1 foot here, 1 foot there. Does that count? Who decides? Some algorithms smooth those out, some dont.