"way over"? Then it sounds like you're using it wrong. It has a weird User Interface. You have to make sure to see the "Set" message before you press "Play". You have to reset the pressure between each tire - a simple - then + will do it. If you don't do this, it will keep filling the second tire more and more until you press "Stop".
The weird UI is partly because it was designed to fill basketballs, beach floats, and other things that don't have a set pressure, as well as tires which do require a set pressure. Just remember to set the pressure explicitly for each tire and you will be fine.
The actual psi number that is shown is consistent but not the most accurate. I fill my tires, then once the dash starts to show the actual pressure I sometimes have to let ~1-2lb out of a few of my tires.
Some aren't as accurate as others. Mine seems pretty spot on, but I've seen some more than 5psi off. That could be considered way off depending on the target.
