The gauge shows oil pressure by yellow bars, its usually up three bars. I was coming home from a job and it dropped to two, and then one, and then the red light came on.
When that happens, my worry level tends to increase.
When we lost the engine in it a few years ago, due to a oil line rupture, the sending unit was actually stuck, and the new engine I bought, its sending unit didn't work correctly either. So in the interest of saving my blood pressure, we installed hose and a standard fluid gauge in the lower cab.
So the whole time the electric gauge was doing its dive toward the cellar, the mechanical gauge was telling me everything is fine. I did pull over and make sure I wasn't puking out oil, just to be sure....