You can't always depend on the zero reading at O pressure. If your gauge has a little pin sticking out of the face of the gauge at the zero pont it prevents the needle from going below zero if the calibration is off. If the needle is pressed against the pin at zero pressure you need to check at another pressure to see if it's calibration is OK.
If there's no pin and it reads zero at 0 pressure it's probably OK.
If it reads above zero at 0 pressure it needs repair or calibration or replacement
Many of these if you exceed the upper pressure by a small margin (maybe 20% or so) are repairable but way too much pressure can straighten the tube and make them useless. But some are pretty delicate almost like repairing an old mechanical watch.
