Was accurate at target (35psi) for our car tires and showed 4lbs less at 65psi for our bikes. So not quite linear; But knowing this, I only intentionally fuel bikes at 4psi. If that wasn't my 'golden spot', unlike some brands this can be adjusted, but be aware that in my experience it can only meet the standard at a certain point, so not 'calibrated' can be. . " with strict rules. the meaning of the term. I really wish it had a lower range gauge (I'm actually very happy that it reads correctly at 35psi, which is what I'll be using it for most) since accuracy is usually a percentage of general range; The longer the range, the less accurate the sensors, usually at the bottom. It's generally legible, but not so good in the dark when it's raining. BTW I could also set it to within about 50psi and then it would be off by about 2lbs - close enough for most people. - for my two uses. I hooked it up to a porter cable compressor/tank combo (ASIN B006CVXGR0) and it greatly increases the compressor's usefulness.