Previously in my post on gauge accuracy I suggested that you could get your pressure gauge checked by visiting a tire store from a tire manufacturer or very large dealer. Well after doing more investigations it turns out I was expecting more from dealers than they actually provide.
Tire dealers are primarily in the business of selling tires and vehicle service. They use gauges every day to inflate hundreds of tires but they do not have ISO calibrated gauges as this would be very expensive and the difference between the gauges they use every day and a calibrated gauge might be measurable but is not really meaningful.
Now this doesn't mean you should not make an effort to confirm your gauge is reasonable accurate the question is "How accurate is accurate enough"? If your gauge is +/- five percent of the inflation pressure you're measuring then you are probably okay, especially if you're running at least five percent above the minimum inflation needed to carry your load as measured in individual tire load scales.
Still, I would suggest you get a digital gauge for your personal "master gauge." They cost as less than $15. Then use that master gauge to check your everyday gauge. Keep your master packed away and not rattling around the bottom of your tool box under the hammer and wrenches where it will get dirty and damaged.
If you check a front tire with the digital master and then your every day gauge and note the difference then when you compare them again maybe a month later you should see the same difference. It is very unlikely for both gauges to go bad the same amount in the same direction at the same time.
If both gauges are within two to three percent when you first get the new digital master you are probably okay. If there is more than a three percent difference then I would check both against some other gauge to learn which is wrong.
Hope this clears things up and sorry if I mislead anyone.