well... the stock gauge is no accurate. it could show zero all the time and youll still have oil pressure.

i put an aftermarket one on my car and at idle when its warm, i get like less than 10 maybe psi, but when i get on it, it goes to like 50 or 60.

if i recall correctly, there is a certain number that mazda says is perfectly fine. its at around like... 10?? i dont know. but its a low number.

 

so your saying that there is something wrong with the sending unit cause the reading is suppose to be less than 30when it's at 800rpm.
and change the gauge too.