gauges

I own fx impact and also a edgun leshiy. I have tried multiple gauges/manometers on the impact from original fx, huma,and wika. All three had accuracy issues against each other and a larger scuba gauge i had tested and use on my fill bottle. I even sent the wika back and was verified by them to be off a few bar. I bought a Leshiy with the electronic/led gauge was off a few bar but very close and had a slow leak so Brian replaced it with a mechanical/analog gauge at my request and its off by a few bar. I do have one huma on my impact for the bottle and another wika on the reg both matching my fill gauge. I guess we cant expect these little gauges to be perfectly precise as they can be purchased reasonably cheap retail. I would assume most airgun manufactures don't make their own gauges and could be made in China. Any thoughts?