Which gauge or indicator is used to know oil pressure ?

In the vehicles having a plunger type gauge, a dialed gauge unit is fitted on the dash board, whose needle moves with the pressure of oil. Nowadays, for knowing the oil pressure, warning light is used. in the vehicles. For this purpose a special type of oil switch is installed. When engine is off and the ignition switch is put on, this light glows. But the moment, engine starts and adequate pressure of oil is built, the light goes off with the oil switch. In other words, if this red indicator light keeps on giving light, it means there is no pressure in oil and there is some fault in lubrication.