Why this crap is always spouted about innacurate gauges purely because they are electric is beyond me.
There is no reason why a lecky one should be any less or more accurate than a regular mechanical one, so long as it has a matching pressure sender, and your regulator part of the alternator works perfectly.
They will normally use either a thermal pressure transmitter and indicator(gauge), where a analogue signal will be produced and represented on a gauge showing pressure, the signal produced is directly proportional to the pressure applied inside a pressure sender by the diaphragm contacts and heater coil.
A more expensive type will use a piezo crystal but where again pressure applied will induce a differing voltage across a fixed value resistor which again is directly proportional to the oil pressure.
I don't think most people are after accuracy down to 1/1000 of a psi, I have el cheapo TIM gauges, that is within 2psi of actual at 13.8 volts which I think is close enough, epecially when you consider the engine has been at that pressure all the time, the only difference is now with a gauge you know it, it worked before with the same pressure.
tabetha