In my garage, I use a Moroso bourdon tube type gauge that's similar to the Motion-Pro but is not liquid filled.
The beauty of such gauges is that that gauge element can be changed to something better.
I will admit I have never confirmed the accuracy of the gauge, and now must find a way to do so!
On the road, I use a digital that is consistent with identical travel gauges for our cars.
A good indicator of gauge quality is repeatability.
If one does 3 - 5 tests in a row and gets lots of scattered results, consider the gauge as being highly suspect and being of the ballpark variety at best.
Air pressure gauges indicate relative air pressure, not absolute.
So, at 5500 ft altitude (Denver for example), a 32 psi pressure gauge reading means an absolute tire pressure that is 2.7 psi softer than at sea level in terms.
Absolute pressure is what supports the tire, not gauge pressure.