Uses the gps for speed and bearing. It does not use compass sensor in device, so you will have to be moving to see any change in direction.
Tap the widget to bring up prefs screen... Options are:
MPH or KM/H display
Font for speedometer reading
Color of speedo and compass
Background color of the widget
Transparency control of that background.
You might not see speed unit change until the next update from the GPS. If the gps is not sending updates, "NO GPS" will be displayed. Updates are requested from your phone at maximum update frequency. When not in car mode, it will also show "NO GPS" as it does not receive gps updates outside of car mode.