+x Warren (Staff) - 10/2/2019 9:40:42 AMAssuming there has definitely been no leaks, then it could be a variation in atmospheric pressure. There is a little rubber grommet on the gauge, gently pierce it to equalise the pressure between the gauge and atmosphere and it should be a bit more accurate. Be careful not to pierce deeply as you can hit the internals which would definitely knock it out of sync.