Your pressure gauge’s accuracy rate will be determined by the specific environmental conditions: barometric pressure of 1013 bar (29.92 Hg) and temperature of 23°C (73.4°F). If the conditions differ from these two factors, it can affect the accuracy rate of your gauge. Also, you can check the pressure of one tire with the tire pressure gauge about which you have a question. Then with another gauge from your friend or neighbor, check the similar tire. In case you get a significant difference in measurements (4 or more PSI) between the two readings, then both or one is inaccurate for sure. If you get the most accurate tire pressure gauge, it has the certification of being accurate.