Our high pressure, dual head pencil gauge is extremely easy to use. Just pop the head onto a valve and take a reading. Plus, we've included 2 valve extenders, so you can always measure your air pressure, even in those hard to reach places. You can improve your gas mileage by around 3.3 percentage by keeping your tires inflated to the proper pressure. Under-inflated tires can lower gas mileage by 0.4 percentage for every 1 psi drop in pressure of all four tires. Properly inflated tires are safer and last longer.