Speedometer GPS - necessary thing not only for the car driver, but for driver of any transport:
• Accurate speed
• Units (km/h or mph)
• Cruise control - speeding warning
• 0-100 Acceleration
• HUD mode. Head-up display – Just enable HUD and put your iPhone or iPad under the windshield. Specially designed HUD interface will display the most accurate speed right on the windshield.

NOTE:
Not compatible with WiFi only iPad or iPod touch.
GPS usage will dramatically reduce device battery life.
GPS is not always accurate due to device hardware sensor limitations.
Make sure that you have location services enabled for the application.
To enable: Settings -> Speedometer -> Location Services