Tire Gauges ALSO can be notoriously inaccurate! The ones that are connected to an air line, and the typical Pocket Gauge, all have a lineal spring that is compressed by the air pressure, to then give a reading. The problem is, the springs ALWAYS fatigue! I take my German MOTOMETER gauge with me to correctly calibrate the pressure when I (or some TIRE TECH) inflates any of my street tires.
Worn gauges read TOO HIGH; it may read 35psi, but in actuality be 25! Especially so with a wide-range gauge, 0-100psi, used on air line inflators.
BUY A GOOD GAUGE!