I purchased the bottom mount pressure gauge from tft, I believe it was last year, and since day one it's been inconsistent. For example, it could read 20psi, turn the pump off and on, then it's at 17 and a few minutes later it will be at 20. Other times it behaves as expected, which would be for it to read 20 again. Sometimes when I turn the pump off, it slowly goes to 0, most of the times it goes straight to 0. Other times when I turn the pump on it slowly rises, most of the times it climbs right to, what I assume, is the correct psi. Did I get a dud? is there something I can do to try to correct it?