I take it your talking about the actual air pressure setting so you don't over power or under power your gun. You could google the company that makes your gun for the exact pressure. I set my PSI at 95lbs for my braid nailers. For the large finish nailer, or construction nailer I set it at 120 PSI. Hope this helps!
The setting for these guns is usually marked on the side of the gun,however if you can't find it I normally set mine at 90 lbs. Yours may be different so I would suggest to start at 90 and see what penetration you get if not enough adjust little by little until you get the head to stop flush with the wood.