As Sospan and others have pointed out the gauge is electrically connected to a sensor , so a reading is dependent upon the quality of the electrical circuit. On my Hotwire system there is no feedback loop to the ecu, but the connector to the sensor is still the weak point.
Once hot, my 1998 car generally idles at about 2/3 bar , and will normally run at about 4/5 at cruising revs. After a Malory Park MSCC track day I noticed the pressure was almost off the scale at any RPM. On checking the connection to the sensor had worked loose , tightening it up put things back to the above figures immediately.
These figures are only applicable to the later "serpentine belt" Rover V8s , the early versions were high capacity oil systems , not high pressure.
A dealer once told me "as long as it has some oil pressure on the gauge it is probably OK" . Must admit that would still be slightly worrying for me to accept.
