This is a nifty little device that attaches to your vehicle's OBDII port under the dash. It is adaptable to most vehicles (visit Scangauge's website to be sure yours is on the list). Interestingly, it interfaces via an ethernet port. I used it on a Ford Taurus, A Mercury Grand Marquis, and a Dodge Caravan. Yes, it displays real time MPG data. It also gives you the average time weighted average MPG. RPM, MPH,and TPS data- no problem. Coolant temperature, Ditto. Manifold absolute pressure depends on the vehicle. Same with intake air temperature. It does not give the actual O2 sensor reading, only if the loop is closed or open. It will definitely teach you skills to improve your fuel economy. Surprisingly, the larger your engine the better you will do because you can take advantage of low rpm high torque situations. I got 29.1 MPG with my Grand Mark using it (Averaged over 65 miles in city, highway and country backroads passing Amish Buggies) Philadelphia to Lancaster, PA. I would have given it 5 stars but the materials it is made with are lightweight and I'm not sure if it will stand the test of time. It is a very useful gadget, and it is a shame we can't hook it up to a laptop to send the data to the state DOT to pass emissions inspection. I suggest ScanGauge look into this, it would probably only take a software upgrade, I know the hardware is up to task. I also suggest they encase it in shockproof rubber to protect it.This is a follow up review  5000 miles out from the last review. I revised the unit to 5 stars. Its durability has proven the test of time and jockeying between 3 vehicles. It sits nicely above the wheel of my V8 Grand Marquis with no significant dash obstruction. It maves easily from vehicle to vehicle an is capable of taking a hit bere or there. It would still be nice to have a shockproof rubber case but I upped my rating to 5 stars both because it held up well and it helped me average between 24-28 MPG country in my Grand Mark. It paid for itself in gasoline already. Anything more is gravy now. The only thing I suggest is a list of OBD codes to go with the unit. It is no longer as easy to find them using google because the mechanics and auto makers want to keep this information proprietary. Google OBD and the first 50 entries are either discussion boards, parts suppliers, or sensor makers. The same happens when you seek out a specific code. You have to dig but you can find what they mean. A list would be nice.