Raptor nitro....how to tell input pressure??

[GDDYUP]

I have an Air America 4500psi Raptor tank for my 68 Classic. It has a gauge on it that tells me how much PSI I have in the tank, IE how much air I have left to shoot. I've seen some posts on here about input pressure to the regulator in which people mention having nitro tanks pre-set to 800-850psi. My tank has an adjustable front reg from the looks of it, but does not have a gauge that tells me what the pressure would be if it is adjusted. There is a "high" and "low" set of ports on the safety side of the tank (it says safety on the opposite side of where the pressure gauge is). Since I'm a complete n00b at this, I have no idea if there is a gauge I can add to the tank that will tell me the input pressure.

Could someone take a few minutes and explain what I need or what I should have on the tank reg in order to set the adjustment properly?

Thanks!

[Tunaman]

You must add aouther 1500 psi gauge in line somewhere before it goes into the gun. Check my sig to see what I have done.