With Bike Display you can also use your iPhone as a bike computer. The current speed is calculated using GPS data from your iPhone. You can also see your current position on a map. And with GPS you get the current altitude above sea level and the direction in which you are moving is shown as a compass needle. For the current tour, you can record the total time and distance covered using a start / stop button.
No data is permanently stored on the iPhone.
The iPhone is best attached to the bicycle handlebar with one of the many silicone holders.