You'd need a real pressure gauge. I'm assuming by the question that you don't have one...I believe most major parts places (AutoZone, O'Reilly's, etc) rent them for nominal fees. Still, you need to know what the pressure is supposed to be. Most engines (I think) run from 12-15 psi at idle, which is subject to variation.
I really wasn't being sarcastic, although reading it I'm quite sure it appears that way. If you're sure, feel free to ignore me - I'm used to it. Heck, I work for the Government. While I may really "be there to help", it's not often perceived that way.