I used an ISSPRO gauge. With the FASS 150 that I have, everyone else is seeing 14-16. Since I am now seeing the same pressure that everyone else with the same setup is seeing, I feel like that is more accurate. Also, I have a little fuel pressure warning light that goes on under 4 PSI. The quad would be saying 0 PSI, but the light wouldn't go on. Now, when the ISSPRO gauge reads below 4 PSI the light comes on. Not to mention, if I was driving around at 0 PSI like the quad said, I would not have been able to accelerate on the highway and I'd have lost the VP44 long ago.