Hi, like others here on the forum I have several tire pressure gauges. And from time to time I compare readings. I have two pencil gauges that I keep in the Lincoln glove box, one is for cars [lower pressure reading] and the other is for trucks. [higher pressure reading] The car one is for my Lincoln and the truck one is for my trailer. I also have the inflater gauge that stays with my home compressor or the portable compressor when towing. I have a high dollar, dual foot, dial gauge, that is accurrate for low and high pressures; I bought this one for my P-30 "Mac Tools" truck with 19.5" wheels. For some reason, these wheels had odd openings and all of the dual foot truck gauges that I tried wouldn't fit correctly. So I had to make a calibrated bend in the air tube of the gauge to make it work. So, what this is all leading to is that if your gauge, or the angle in which you hold it, doesn't make a good seal, you will not get a correct reading. Anytime I use my gauges, and I know it didn't seal correctly, I do it again making sure it was a good seal, giving me a correct reading.