If you are referring to your oil pressure guage in the car I believe the technical assumption is if it goes up as the revs rise all is OK. In other words the guage is not accurate. I dont know the specification for an accurate measurement using a suitable guage.
When cold, if the gauge and sensor are working correctly, the gauge should read at the top of the range, on the far right. When the engine is at operating temperatures, at idle it will be below the left side low mark. On mine, when cruising at 3000 RPM, the gauge sits right about 50#. GUBI is right, usually the oil pressure sending unit goes bad.
Waste of time and money changing the gauge or sender unit. Neither will ever be accurate. If the gauge goes up with engine rpm then its fine. Alfa engines have excellent oil systems (exclude boxer) so If you have a oil pressure issue your going to know about it because it will be something very bad. If you want to accurately monitor oil pressure get yourself a quality after market sender unit and gauge.
The 'rule of thumb' for oil pressure is about 10 psi/1000rpm - up to the relief valve's set point.
As others have stated, the Alfa gauges are more 'general indicators' than absolute measurements. With a cold engine, oil pressure should show on the gauge within a few seconds of starting and it will typically be near the relief's valve set point even at idle. Once fully warmed up, oil pressure at idle will be much lower - some Alfa gauges will point to barely above zero. If your car has one and the low oil pressure warning light is not lit, then I wouldn't worry about it. If oil pressure should ever register very high I'd make sure the sender is OK (they are the weak link in the system) and if so, then I'd worry the relief valve is stuck open (not good).
ncng... a oil leak wont cause a loss of oil pressure unless its horrific. Your gauge could be inaccurate for so many reasons ie: sender unit, loose connectors, bad earth ect ect. If you have an oil pressure issue you will know about it. Death rattle and eventual engine failure. I kind of look at my oil pressure gauge as an oil temp gauge. When its reading bugger all at idle the oil is nice and warm. As an anecdote i was having fun on a b road years ago when the wire from the oil sender came off giving me a bad oil pressure signal...my heart stopped as I pulled over only to be relieved that the spade terminal was loose.
Just for comparison: I have "great pressure" on the gauge when cold between 55-75 and almost none when warms up. My pressure in the engine is fine though. If it shows when cold and moves with revs, you should be ok.
My oil pressure is between 10 and 100 at about 3 times per second non stop. The needle looks like a mexican jumping bean. I tried two gauges, two different sending units and two different Engines. Actually it pegs out over 100 when its cold slowly comes down within 5 minutes then starts it dancing show for the rest of the day. Guess I just gotta live with it.