I recently bought a new front tyre (stuck with oem as I got 11,000kms out of the last one). And as I always do when I go to the tyre shop I take all three of my gauges in and ask them to check them against their equipment. I have a pen style gauge, round pressure and depth checker and another round one that attaches to my compressor. When I had my gauges last checked only one was spot on (the others were only out by a few pounds). Which one was the best?
The one I got for free when I got new tyres on my truck. The pen style gauge like the one in the picture below. The guys at the tyre shop were not surprised. They said, in their experience, these type hold their accuracy far longer than the round type and can handle more abuse too as they have fewer working parts. Once you know how it reads (might be a pound or two off straight from the shop) they rarely loose accuracy. So my suggestion is get a couple of this type. Usually they are cheaper too.