"Idiot light" vs. Oil Pressure Gauge

YES both the light and a mechanical gauge UNDER THE DASH NOT UNDER THE HOOD. By the time the light goes on much of the damage is done. Changes in pressure as things START to go wrong can be seen as changes in typical gauge readings. Fluctuation in the needle can indicate low oil levels after pan damage or other oil loss on the road that would never show up on the light. I can't even conceive of installing a new engine without installing a mechanical gauge inside the car before turning it over.