I can't believe I have never had one of these! We all inflate to the perfect pressure, but then the board or kayak goes in the water and we don't take into account the water temperature or mid day sun, which can change the PSI significantly enough to cause unnecessary stress on the seams. I often leave my board inflated for a few days, and sometimes I wonder if that extra drag is from under-inflation or just a low energy day. Never again - the AirCap is hard to miss and always accurate. A brilliant accessory!