Fuel pressure gauge

So i have two gauges. I have a small mechanical pressure gauge on the the regulator in the engine bay. I also have an electric autometer pressure gauge in the cab. Cab reads 8.5 psi and the one on the regulator says 6.5 psi. Here is why i m asking. I have been fighting a rich idle and i set the fuel pressure by the gauge on the regulator but i'm thinking its not right and i am over pressurizing the carb causing the rich idle because the electric gauge is saying 8.5 which i am now thinking is correct. Any thoughts?