Not only does the Scan Gauge calculate and display dozens of parameters like miles per gallon, gallons per hour, total trip cost, closed loop status and engine temperatures, it can also be programmed with vehicle specific gauges for your particular vehicle. For example, for a Chevy Venture, it will display horse power, engine torque, air/fuel ratio, transmission temperature and even an obscure parameter called “knock retard”, (how many degrees of ignition time advance must be removed to compensate for low octane fuel, thus preventing engine knocking). For hybrid vehicles, the Scan Gauge will display "state of charge" and the regenerative charge rate of the battery system. 

Efficient driving habits will save you money at the pump in exchange for a slight increase in commute time. 

For me, slower acceleration and reduced cruising speed adds 3 additional minutes to my 20 mile commute. In exchange, I only have to pay to fill up for gas tank every 4 weeks instead of every two and a half. Not a bad compromise in my opinion.