Do not buy this if you are a professional technician where time is money as most of us are not paid by the hour but by performance. The display takes a few seconds to turn on power when connected to the valve stem and then a few more seconds to read the pressure. Even if you turn it on manually by pressing the power button, it still reads the pressure painfully slowly. Also, the tire deflation valve is too sluggish, they have to increase the opening, it takes a good ten seconds to deflate a few kilos on a small car tire. Also, I've noticed that when I adjust the pressure, disconnect and reconnect the chuck, the pressure reads about 2 pounds less each time. You're better off having a .50 cent tire gauge and an air cartridge, or spend about $20 more and get a better gauge.