Where is personal responsibility? It's tossed out the car window at 70 MPH. Gas prices are brain-numbingly, irritatingly high. Yet we putter through traffic in our 250-horsepower cars, drinking gasoline like I drink Tang.

I know my limits. I can't convince America to stop driving big gas-hungry cars and put more automotive research towards fuel efficiency. But I'll still fulfill my debt to society with advice: Change your driving habits and save gas. A great tool for doing so is the "ScanGauge II".

The ScanGauge is a small box packed with electronics. Usable in any car made in 1996 or later, it plugs in to your car's "OBD II" port, a special plug used for computer diagnostics. The ScanGauge uses this diagnostic data to give us real-time information about our car's performance, including mileage: While driving, the ScanGauge reads your car's speed, load, throttle position and other factors, and computes your current miles per gallon.

Below are pictures of the ScanGauge in action:

This MPG display lets you dynamically improve driving. See how mileage changes as you accelerate, climb and descend hills, or cruise the highway. Fine-tune your driving. Reduce bad habits, use less gas.

For this ScanGauge II review, setup was simple, no wiring or batteries needed: Plug it in, and start your car.

The mileage monitor isn't ScanGauge's only tool. It's also an OBD-II code reader, allowing you to read and clear problems caused by "Check Engine" lights. Report trip info, like overall mileage, average speed, driving distance and fuel used.

After using the ScanGauge II in my 2002 Saturn SL, here's what I learned:

During acceleration, letting up on the pedal just one inch increases mileage by 15 MPG. Turning on air conditioning drops mileage by 4 MPG. I always thought coasting in neutral improved mileage (versus leaving the car in gear), but the ScanGauge tells me it makes no difference. Cruise control is usually good, but wastes too much gas on hills.

The ScanGauge II comes with geek-friendly features: It's upgradeable, so future improvements (like PC communications) can be installed. Car hackers can send OBD-II commands to their cars' computers, tweaking to improve performance. Customize many options (including the screen backlight, with 63 different color choices).

At $170, it's not cheap. But learn from it, and it does pay for itself: I recorded mileage before and after buying my ScanGauge. In city driving, using it to adjust my driving habits, I averaged 24 MPG before the ScanGauge and 27 MPG after. I fill my tank about once every five days. Assuming gasoline is $3 per gallon, I'll need just over seven months to save $170 in gas.

Some commercials start pitches by saying "in times like these…" Half-heartedly alluding to the economy, global terrorism, or just plain persnicketyness, they really mean "whatever unspecified thing bothers you, we can indirectly help."

Not so with the ScanGauge. I'll be very specific: "In times like these, with horrible gas prices, the ScanGauge can help you save gas money by adjusting your driving habits."