Most vehicles have this capability through the engine-management computer to calculate similar information, but automakers don't always offer a driver display.
Now the aftermarket is responding with back-seat drivers that provide a variety of vehicle information and behavior. The one shown is called ScanGauge, but there are others from Davis Instruments called CarChip.
The devices operate differently. ScanGauge provides a display while CarChip can sound an alarm if fuel economy dips below preferred levels. CarChip also allows the driver to download the data to a personal computer.
Installation is easy and prices vary.