Upon purchase of a liquid filled air gauge, the user may find a variance in the readings from some known accurate gauge. This variance could be caused by the atmospheric pressure differentials from the outside air to the inside of the dial housing . This pressure difference, if great enough, can cause some gauges to read incorrectly as much as 5psi.

This pressure difference can be caused by the altitude being greatly different from where the gauge was assembled, transport via airplane, or simple travel from low altitude to high (sea-level to mountainous areas).This change can also be created by large differences in temperatures. For instance, the gauge is stored in and air conditioned building. It is used in the morning, and left outside for a couple of hours and the sun heats it up 30 degrees. You check the same pressure and could get a different reading.

There is a simple way to correct this issue. If your gauge has a continuous rubber shock absorbing boot, carefully remove it. Now you should have the bare dial housing exposed. You will find a small rubber plug (normally at the top of the dial). Your gauge may also have the rubber or plastic plug exposed via a pre-cut hole in the rubber booth.Cautiously remove this plug (if the plug is plastic is may not come completely out of the gauge and that is normal) and the gauge will equalize to atmospheric pressure. Replace the plug and rubber boot.

Your gauge should be fully operational within the manufactures tolerance.

Warning: If you have dropped your gauge or it has sustained a great shock or jarring, chances are your gauge  has been knocked out of tolerance (the internal components damaged). There is no recalibration for most gauges and your best bet is to simply purchase new one.