Flowscan is a brand of fuel metering sensors and displays.  The system monitors the flow to the engine and from the engine to the tank to determine the fuel usage.  It then uses GPS data to determine consumption performance.  It is a great tool for evaluating fuel efficiency.  The cost is about $1,000 plus installation.  A less expensive system with the sensors and an analog gauge which displays only the gallons per hour is less expensive at about $700 plus installation.