A gauge is a precision artefact that spends most of its life doing nothing. The damage that takes it out of tolerance usually happens during that time: a burr from being dropped into a drawer, a rust bloom from a humid weekend, a flattened edge from lying against another gauge.
Keep gauges in a dedicated case with individual recesses, in a room that stays above the dew point. Vapour phase inhibitor paper in the case is cheap and effective for steel. Never store a gauge with the part it gauges, because chips and dust from the parts migrate into the case.
Handle by non-functional surfaces and wipe the functional surfaces before and after use. Skin oils are mildly acidic and hold moisture against the steel. Do not use the gauge to check a part that is still warm from a process; the thermal shock is a minor issue but the moisture condensation that follows is not.
A ten second visual check under a loupe catches burrs, corrosion pits and chips. Any of those on a functional surface means the gauge comes out of service, not that it is used carefully. The cost of a spare gauge is far below the cost of a recall caused by a no-go member that had been flattened for a year.
