dash oil gauge

hi all i know this might seem like a daft question but here goes.
the oil gauge on the dash is it a oil temp gauge or a oil pressure and if its an oil pressure is it in psi or bar the reason i want to know this is the engine is a 2.8 td isuzu and like all things landrover/isuzu it doesnt match thus im thinking of replacing the oil and water temp with after market gauges

Wont be std land rover so must already be an aftermarket unit.
Assuming its in a defender?



Lynall