How accurate are Ebay cheap digital oil pressure gauges

[pimpin81]

I was wondering how accurate ebay digital oil pressure gauges are.. The one i have is saying 0 psi at idle but when i pull the oil cap off i have tons of oil in the head. Its almost like when its around 15psi at idle it doesn't want to read accurately. When i do a pull its at like 68psi give or take and revs to 4k usually net around 40 psi according to the gauge, i dont have the dash gauge anymore this was supposed to be a more accurate replacement but now I'm second guessing everything. The sender is in the stock senders location btw.

Here's my theory if i have lots of in the head to where is spraying out because the cam is saturated in oil i know i have oil pressure everywhere else because that is the farthest it travles. in the engine.

So whats up with that ?

 

[DSM98GSX]

Normally I would say you get what you pay for...but I dont know what gauge brand you got. There could be a number of things that are making it "malfunction." Check to see if the gauge actually reads low enough for when your car is at idle...ie did the gauge manufacturer design the sensor to only read above 15psi? Also, if you happen to have a spare gauge or a friends, try that combination too. Hope this kinda helps. Good luck.