Altimiter, It's Not

I recently bought a heart rate monitor for use when I ride. It's got spedometer, trip and odometer capabilities, too, so I don't lose anything over the traditional bike computer. This fancy-pants model actually has a barometric altimeter, as well. After a bit of wrangling with Google Earth, I managed to find my house (including some odd pool-looking thing in the back yard), and get an approximate altitude: 58m.

When I left for a ride today, I dutifully programmed in the starting altitude, to get an accurate profile for the workout data. When I got home, I found that the same spot at which I had set the altitude in the first place was now only 54m above sea level! I guess the alternate post for this article could be "My House Is Sinking".