quad-4 oil question

Hi I am new here, just a simple question for now
I have a 1995 grandam se, quad-4
now when I first got the car, I noticed that the oil pressure gauge was about 3/4 of the way up. It was at that level no matter what. I just thought it was normal. When I got the first oil change, is when I noticed something differnt. Now the oil pressure gauge jumps according to the rpm of the motor, as the motor warms up, and has been running for a while, the oil presure slowly goes down, to the piont when I am doing 60+mph and it is not even at the half way mark.
I am wondering if this is normal or not?
if not, what is causeing this?
if so, then why was it just sitting in one place when I first got it?

Well The spec for oil press is 15 min psi @ 900 RPM and 30 PSI @ 2500 RPM. You might want to have the press checked with a guage. If it isn't a guage problem than you Main bearings are probably getting worn down.