M8 mini gauge?

Heck I just bought a 5$ analog gauge that is actually really spot on in terms of accuracy, I am impressed. Reads 2150 psi and my set point is 2150 psi.

They're all hit and miss though. But even my last gauge it replaced is accurate and read about the same.

You can pop the lens off (kind of a pain) and re-calibrate them using your fill gauge if its more precise. Worth doing if you're that desperate, but I'd order another in case, and hey you may win the lottery with it. Just browse aliexpress. These are only 5$ m8 gauge 350 bar

-Matt