Over the years I have accumulated various devices to help maintain the correct pressure in the tires of my cars, but nothing quite compares to this device in terms of simplicity and apparent accuracy. Throw away all mechanical pressure gauges and air cartridges as they are obsolete! This device can do everything! I just repaired a leak (a nail in a tire) on my wife's Altima and needed to get the pressure right. My old digital meter had a dead battery and the cartridge wouldn't work properly; So I ordered this combo tool. How easy can it be? Inflate the tire with some air, attach this device to the air hose (don't forget to turn on the air compressor) and attach it to the tire's stem. Then it displays the tire pressure; Squeeze the large chrome lever to add air, release the lever and your current pressure will be read; If too much, press the brass button to deflate, if not enough, just add more. There is no tool changing to perform different functions. Super easy, quick and easy.