Have you ever wondered, how fast are you traveling down in the subway?. With Subway Speed your iPhone/iPod Touch uses internal accelerometers to calculate your instant speed. NO GPS needed. If you have a 1st generation iPhone or any iPod Touch, this application is as good as it gets if you need a speedometer.
The Challenge:
Make sure you hold your iPhone/iPod Touch completely steady while speed is being sensed (try resting your device over your lap or on a unoccupied seat next to you). Be sure to start speed sensing when your vehicle is full stopped. Accelerometers are very sensitive to any tilt, movement or changes in direction/slope of your vehicle. The challenge is to keep your device as steady as possible, and when your vehicle has stopped in the next station, the residual speed must be around 0.
Disclaimer
This is not a precision tool, nor a real speedometer. Its just an entertainment application that is intended to keep you busy on those tedious subway rides. Any tilt or change in slope or direction of movement induce false accelerations, that are impossible to filter due to the lack of an internal gyroscope.