We'll go through the list....
You could have a bad gauge
bad sender
shorted wire (ground short will cause high reading)
You could also have 100 PSI oil pressure. I've had engines that would go to 100+ PSI on a cold start, especially with a high viscosity oil.
I personally like electric gauges.... I never liked the plastic oil line coming into the car that most mechanical oil pressure gauges have... Just a leak away from ruining a carpet. But, as a rule, the mechanical gauges tend to be more accurate and repeatable.
Here's what you can do... Buy a mechanical gauge and just hook it up in the engine compartment. If the two agree... well... chances are you have 100PSI oil pressure. If they don't, one of the gauges is wrong.
