huma regulator question.

Hello everyone, I'm new to the page and have a question I hope someone can help me answer. I might understand this wrong, but I have a .22 cal Benji marauder and I want to get a huma regulator for it and use my stock psi gauge. my question is, it says the huma regulator reads the regulated pressure and not the psi in the air cylinder itself. so, if I use a hand pump, how do I know how much pressure is in the cylinder? I may not understand cause i am new tp pcps but wanted to check before ordering. any info helps! thanks.