Stock Boost gauge accuracy

I compared mine with a couple of other gauges and it was within a pound of them.

ok, so mine hitting over 15 means my car isnt running 12 psi like it should.

Umm...yeah. As long as the needle is centered pretty good, they aren't any less accurate than typical Autometer in my opinion. The lack of tick marks on some of them make them tough to read, though. I've got both in my CSX and extrapolating where I would expect to see 20psi, they are pretty close.

I see what you mean, there is only one little mark in between 10psi and 15psi