Apologies for bursting everyone's bubble but mine is the most advanced of all tire pressure gauges
in fact I couldn't care less about real tire pressure. I just use this pen gauge as an index really. I roughly set tires slightly above the mfg specs and then depressurize until the ride feels right for me and the car. Then recheck with the same pen and try to stay in that range/index.
I waste my money on Happy-O-Meters instead
