My old tire gauge died- battery dead, not replaceable. So I went to Auto Zone for a new one.

They had three- a Slime brand (yeah, I know, weird name, but I bought one of their air pumps and it works fine) 0-150 psi, 2 lb accuracy, 0-99 1 lb accuracy and a $2 pencil-type one that works on pressure, not electricity.

Bought the first and the third (figuring for two bucks why not have a back-up).

They disagree consistently by 2 lbs (Slime's 2 lbs lower).

Any guess which one's right? Or how I'd go about testing them?

 

I use this one AutoZone spec says it's calibrated.

I would take your gauges to your trusted mechanic and compare readings with one of theirs.