When we first tried this thing we taped it to the tire and it read 34 my daughter always thought air was getting in and pressed the latch and the tire. drained πππππ€£π€£π€£π€£π€£ up to 18. We needed air so we drove to the fire brigade in our city where the valve was properly explained and demonstrated to us. inflate a tire. It reads tire compression and air volume. It was a really educational experience. Worth buying. It really works! Investing in your car is worth it. ππΌ