Used to check tire pressure after airing. I use 9psi front and 8psi rear for rock crawling. This pressure gauge is perfect because not only does it accurately read your psi, but if it's a little higher, push the exhaust valve and the tire pressure will drop right where you want it. The light sensor works surprisingly well. Even in broad daylight when airing from the shady side of the car. When I removed the gauge from the valve stem, it fell out of the box half a pound per square inch. The company emailed me to see if I liked the sensor. I told them about my concerns. They emailed me explaining that there might be dust in the valve and how to clean it. I did as they said and it works like a charm! I forgot to reset the gauge before putting it in the glove box and it held pressure all day until I checked my tires again. Excellent merit!