Pressure gauge on fermenter and regulator don't match by a lot. Which is right? How do I know?

[MidnightRising]

I just recently purchased a Spike Flex+ along with its pressure transfer equipment, which included this nifty pressure gauge and PRV. The thing is it comes nowhere near close to the same reading as my (admittedly several year old) regulator gauge. If I set my regulator to 10PSI, Spike's gauge reads 5PSI. Now normally this wouldn't be the end of the world because for a pressure transfer it makes little difference, but I also purchased their carb stone and to get it to the required 9PSI @ 38F to carb to 2.2 volumes according to Spike's gauge I have crank it up to about 18PSI according to my regulator-- and this thing is rated for 15PSI. If I trust my regulator and it turns out the fermenter is right then I've got a terribly undercarbed beer and have to wait another 5+ days to have it be drinkable. If I trust the fermenter's regulator I have a way overcarbed beer (or, in the absolute worst case scenario, a pressure bomb).

Is there some way I can test these things at home, or is there one that I should definitely trust over the other?

 

[Bilsch]

Spend some money and buy an American made gauge. These Chinese made ones anymore are so far off it's ridiculous.

 

[Jtvann]

Remember wetting pressure. I suggest that you test out the outside gauge accuracy by filling without any restrictions. The carb stone has restrictions to it, effectively reducing the pressure going through it.

Add some pressure to your flex+ through the blow off arm, or racking valve. See what your pressure reads in both your regulator and pressure gauge.

Pull off your carb stone next brew and submerge it in a glass of water. Hook your CO2 line up and slowly increase pressure. Note when you first see bubbles come out. I’m betting that’s somewhere close to 5 psi for you. Sounds a little high, but not unbelievable. Subtract your wetting pressure from your regulator reading to get what’s actually going into your beer.

 

[Vale71]

What he said plus with time I've come to regard mechanical pressure gauges as pure garbage. No matter what their accuracy class is once they leave the factory and get banged around travelling halfway across the world their readings are totally unreliable. Tha's why I started using electronic manometers only and have never regretted my decision...