Another option is to make an inline pressure gauge with a steel T fitting threaded in the middle for a gauge and on both ends for QD fittings, that has an accurate analog or digital gauge on it. You can simply insert it inline with the whip for whatever tank, pump or compressor you are using at the time when filling guns or tanks and always know the actual pressure going into the gun or tank.
I currently have three gauges that are inline when filling guns from the co9mpressor. One on the compressor, one on the huge filter assembly which I leave pressurized at all times, and one on the gun. They all give different readings. The difference between the highest and the lowest of the three can be as much as 200 PSI. The gauge on the filter assembly is a nice reminder that the whole thing is still under pressure so I don't try to open it up to change a filter or some beads. Until an inline filter built, I have used the highest quality gauge I have to "calibrate the others and have the offsets noted on a piece of white artists tape right next to the outlier gauges.